RE: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card
> card
>
> On Fri, Sep 09, 2022 at 09:21:30AM +, Winkler, Tomas wrote:
> > > >
> > > > > -Original Message-
> > > > > From: Greg Kroah-Hartman
> > > > > Sent: Friday, September 09, 2022 09:16
> > > > > To: Ceraolo Spurio, Daniele
> > > > > Cc: intel-...@lists.freedesktop.org;
> > > > > dri-devel@lists.freedesktop.org; Winkler, Tomas
> > > > > ; Lubart, Vitaly
> > > > > ; Teres Alexis, Alan Previn
> > > > >
> > > > > Subject: Re: [PATCH v4 06/15] mei: pxp: support matching with a
> > > > > gfx discrete card
> > > > >
> > > > > On Thu, Sep 08, 2022 at 05:16:03PM -0700, Daniele Ceraolo Spurio
> wrote:
> > > > > > From: Tomas Winkler
> > > > > >
> > > > > > With on-boards graphics card, both i915 and MEI are in the
> > > > > > same device hierarchy with the same parent, while for discrete
> > > > > > gfx card the MEI is its child device.
> > > > > > Adjust the match function for that scenario by matching MEI
> > > > > > parent device with i915.
> > > > > >
> > > > > > V2:
> > > > > > 1. More detailed commit message 2. Check for dev is not null
> > > > > > before it is accessed.
> > > > > >
> > > > > > Signed-off-by: Tomas Winkler
> > > > > > Signed-off-by: Daniele Ceraolo Spurio
> > > > > >
> > > > > > Cc: Vitaly Lubart
> > > > > > Cc: Greg Kroah-Hartman
> > > > > > Reviewed-by: Alan Previn
> > > > > > ---
> > > > > > drivers/misc/mei/pxp/mei_pxp.c | 13 ++---
> > > > > > 1 file changed, 10 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/misc/mei/pxp/mei_pxp.c
> > > > > > b/drivers/misc/mei/pxp/mei_pxp.c index
> > > > > > 17c5d201603f..afc047627800
> > > > > > 100644
> > > > > > --- a/drivers/misc/mei/pxp/mei_pxp.c
> > > > > > +++ b/drivers/misc/mei/pxp/mei_pxp.c
> > > > > > @@ -159,17 +159,24 @@ static int
> > > > > > mei_pxp_component_match(struct
> > > > > device
> > > > > > *dev, int subcomponent, {
> > > > > > struct device *base = data;
> > > > > >
> > > > > > + if (!dev)
> > > > > > + return 0;
> > > > >
> > > > > How can that happen?
> > > > >
> > > > > > +
> > > > > > if (!dev->driver || strcmp(dev->driver->name, "i915") ||
> > > > >
> > > > > That's crazy to assume, but whatever :(
> > > > Explained here:
> > > > https://lore.kernel.org/all/20220418175932.1809770-2-
> > > wonchung@google.c
> > > > om/
> > >
> > > Still crazy :(
> > >
> > > >
> > > > >
> > > > > > subcomponent != I915_COMPONENT_PXP)
> > > > > > return 0;
> > > > > >
> > > > > > base = base->parent;
> > > > > > - if (!base)
> > > > > > + if (!base) /* mei device */
> > > > >
> > > > > Why does this mean that?
> > > > >
> > > > > Where is that documented?
> > > > >
> > > > > > return 0;
> > > > > >
> > > > > > - base = base->parent;
> > > > > > - dev = dev->parent;
> > > > > > + base = base->parent; /* pci device */
> > > > >
> > > > > Again, why is this the case?
> > > > >
> > > > > > + /* for dgfx */
> > > > > > + if (base && dev == base)
> > > > > > + return 1;
> > > > > >
> > > > > > + /* for pch */
> > > > > > + dev = dev->parent;
> > > > >
> > > > > You are digging through a random device tree and assuming that
> > > > > you
> > > "know"
> > > > > what the topology is going to be, that feels very very fragile
> > > > > and ripe for problems going forward.
> > > >
>
Re: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card
On Fri, Sep 09, 2022 at 09:21:30AM +, Winkler, Tomas wrote:
> > >
> > > > -Original Message-
> > > > From: Greg Kroah-Hartman
> > > > Sent: Friday, September 09, 2022 09:16
> > > > To: Ceraolo Spurio, Daniele
> > > > Cc: intel-...@lists.freedesktop.org;
> > > > dri-devel@lists.freedesktop.org; Winkler, Tomas
> > > > ; Lubart, Vitaly ;
> > > > Teres Alexis, Alan Previn
> > > > Subject: Re: [PATCH v4 06/15] mei: pxp: support matching with a gfx
> > > > discrete card
> > > >
> > > > On Thu, Sep 08, 2022 at 05:16:03PM -0700, Daniele Ceraolo Spurio wrote:
> > > > > From: Tomas Winkler
> > > > >
> > > > > With on-boards graphics card, both i915 and MEI are in the same
> > > > > device hierarchy with the same parent, while for discrete gfx card
> > > > > the MEI is its child device.
> > > > > Adjust the match function for that scenario by matching MEI parent
> > > > > device with i915.
> > > > >
> > > > > V2:
> > > > > 1. More detailed commit message
> > > > > 2. Check for dev is not null before it is accessed.
> > > > >
> > > > > Signed-off-by: Tomas Winkler
> > > > > Signed-off-by: Daniele Ceraolo Spurio
> > > > >
> > > > > Cc: Vitaly Lubart
> > > > > Cc: Greg Kroah-Hartman
> > > > > Reviewed-by: Alan Previn
> > > > > ---
> > > > > drivers/misc/mei/pxp/mei_pxp.c | 13 ++---
> > > > > 1 file changed, 10 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/drivers/misc/mei/pxp/mei_pxp.c
> > > > > b/drivers/misc/mei/pxp/mei_pxp.c index 17c5d201603f..afc047627800
> > > > > 100644
> > > > > --- a/drivers/misc/mei/pxp/mei_pxp.c
> > > > > +++ b/drivers/misc/mei/pxp/mei_pxp.c
> > > > > @@ -159,17 +159,24 @@ static int mei_pxp_component_match(struct
> > > > device
> > > > > *dev, int subcomponent, {
> > > > > struct device *base = data;
> > > > >
> > > > > + if (!dev)
> > > > > + return 0;
> > > >
> > > > How can that happen?
> > > >
> > > > > +
> > > > > if (!dev->driver || strcmp(dev->driver->name, "i915") ||
> > > >
> > > > That's crazy to assume, but whatever :(
> > > Explained here:
> > > https://lore.kernel.org/all/20220418175932.1809770-2-
> > wonchung@google.c
> > > om/
> >
> > Still crazy :(
> >
> > >
> > > >
> > > > > subcomponent != I915_COMPONENT_PXP)
> > > > > return 0;
> > > > >
> > > > > base = base->parent;
> > > > > - if (!base)
> > > > > + if (!base) /* mei device */
> > > >
> > > > Why does this mean that?
> > > >
> > > > Where is that documented?
> > > >
> > > > > return 0;
> > > > >
> > > > > - base = base->parent;
> > > > > - dev = dev->parent;
> > > > > + base = base->parent; /* pci device */
> > > >
> > > > Again, why is this the case?
> > > >
> > > > > + /* for dgfx */
> > > > > + if (base && dev == base)
> > > > > + return 1;
> > > > >
> > > > > + /* for pch */
> > > > > + dev = dev->parent;
> > > >
> > > > You are digging through a random device tree and assuming that you
> > "know"
> > > > what the topology is going to be, that feels very very fragile and
> > > > ripe for problems going forward.
> > >
> > > I don't think it is random.
> >
> > Today it is one specific way, but how do you know this always will be this
> > way?
> >
> > > > How do you ensure that this really is they way the tree is for ALL
> > systems?
> > >
> > > Yes we take the topology assumption in PCI hierarchy.
> > > There is a case where both GFX and MEI are in PCH and you cannot stick
> > additional PCI extender or anything else there.
> > > And case where MEI is child on a standalone graphics card
RE: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card
> >
> > > -Original Message-
> > > From: Greg Kroah-Hartman
> > > Sent: Friday, September 09, 2022 09:16
> > > To: Ceraolo Spurio, Daniele
> > > Cc: intel-...@lists.freedesktop.org;
> > > dri-devel@lists.freedesktop.org; Winkler, Tomas
> > > ; Lubart, Vitaly ;
> > > Teres Alexis, Alan Previn
> > > Subject: Re: [PATCH v4 06/15] mei: pxp: support matching with a gfx
> > > discrete card
> > >
> > > On Thu, Sep 08, 2022 at 05:16:03PM -0700, Daniele Ceraolo Spurio wrote:
> > > > From: Tomas Winkler
> > > >
> > > > With on-boards graphics card, both i915 and MEI are in the same
> > > > device hierarchy with the same parent, while for discrete gfx card
> > > > the MEI is its child device.
> > > > Adjust the match function for that scenario by matching MEI parent
> > > > device with i915.
> > > >
> > > > V2:
> > > > 1. More detailed commit message
> > > > 2. Check for dev is not null before it is accessed.
> > > >
> > > > Signed-off-by: Tomas Winkler
> > > > Signed-off-by: Daniele Ceraolo Spurio
> > > >
> > > > Cc: Vitaly Lubart
> > > > Cc: Greg Kroah-Hartman
> > > > Reviewed-by: Alan Previn
> > > > ---
> > > > drivers/misc/mei/pxp/mei_pxp.c | 13 ++---
> > > > 1 file changed, 10 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/drivers/misc/mei/pxp/mei_pxp.c
> > > > b/drivers/misc/mei/pxp/mei_pxp.c index 17c5d201603f..afc047627800
> > > > 100644
> > > > --- a/drivers/misc/mei/pxp/mei_pxp.c
> > > > +++ b/drivers/misc/mei/pxp/mei_pxp.c
> > > > @@ -159,17 +159,24 @@ static int mei_pxp_component_match(struct
> > > device
> > > > *dev, int subcomponent, {
> > > > struct device *base = data;
> > > >
> > > > + if (!dev)
> > > > + return 0;
> > >
> > > How can that happen?
> > >
> > > > +
> > > > if (!dev->driver || strcmp(dev->driver->name, "i915") ||
> > >
> > > That's crazy to assume, but whatever :(
> > Explained here:
> > https://lore.kernel.org/all/20220418175932.1809770-2-
> wonchung@google.c
> > om/
>
> Still crazy :(
>
> >
> > >
> > > > subcomponent != I915_COMPONENT_PXP)
> > > > return 0;
> > > >
> > > > base = base->parent;
> > > > - if (!base)
> > > > + if (!base) /* mei device */
> > >
> > > Why does this mean that?
> > >
> > > Where is that documented?
> > >
> > > > return 0;
> > > >
> > > > - base = base->parent;
> > > > - dev = dev->parent;
> > > > + base = base->parent; /* pci device */
> > >
> > > Again, why is this the case?
> > >
> > > > + /* for dgfx */
> > > > + if (base && dev == base)
> > > > + return 1;
> > > >
> > > > + /* for pch */
> > > > + dev = dev->parent;
> > >
> > > You are digging through a random device tree and assuming that you
> "know"
> > > what the topology is going to be, that feels very very fragile and
> > > ripe for problems going forward.
> >
> > I don't think it is random.
>
> Today it is one specific way, but how do you know this always will be this
> way?
>
> > > How do you ensure that this really is they way the tree is for ALL
> systems?
> >
> > Yes we take the topology assumption in PCI hierarchy.
> > There is a case where both GFX and MEI are in PCH and you cannot stick
> additional PCI extender or anything else there.
> > And case where MEI is child on a standalone graphics card this is set
> > in software so topology is not going to change unless we rewrite
> everything. Be happy to hear your insights.
>
> This is ripe to break in the future if someone makes a differently structured
> device as there is nothing forcing the current layout to always be this way by
> hardware designers.
>
> The goal of the driver model is to NOT have these types of hard-coded
> topology assumptions because, supprise, assumptions like this have always
> come back to bite people in the end.
>
> This is your driver, so that's fine, but really this feels very very wrong
> and you
> will have a hard time guaranteeing that this will always be this way for the
> next 20+ years of hardware designs. So why not do it properly from the
> beginning and pass in the correct pointers to different places?
>
> There is a very good reason that the driver model/core does not make it easy
> to determine what type of device a 'struct device *' is, because you shouldn't
> have to rely on that type of thing ever. You are taking it one step further
> and
> just assuming that you know what the type is here, with no real way to
> ensure that this is the case.
>
> In short, this feels like a very bad design as it is very fragile.
I believe I understand your concern but I would need to invent another
addressing scheme to associate hw components that are already
addressable by let say PCI hierarchy. We've changed two subsystems for this
work
components and aux bus already. So let's have some fun in the future.
Thanks
Tomas
Re: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card
On Fri, Sep 09, 2022 at 06:51:21AM +, Winkler, Tomas wrote:
>
>
> > -Original Message-
> > From: Greg Kroah-Hartman
> > Sent: Friday, September 09, 2022 09:16
> > To: Ceraolo Spurio, Daniele
> > Cc: intel-...@lists.freedesktop.org; dri-devel@lists.freedesktop.org;
> > Winkler, Tomas ; Lubart, Vitaly
> > ; Teres Alexis, Alan Previn
> >
> > Subject: Re: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete
> > card
> >
> > On Thu, Sep 08, 2022 at 05:16:03PM -0700, Daniele Ceraolo Spurio wrote:
> > > From: Tomas Winkler
> > >
> > > With on-boards graphics card, both i915 and MEI are in the same device
> > > hierarchy with the same parent, while for discrete gfx card the MEI is
> > > its child device.
> > > Adjust the match function for that scenario by matching MEI parent
> > > device with i915.
> > >
> > > V2:
> > > 1. More detailed commit message
> > > 2. Check for dev is not null before it is accessed.
> > >
> > > Signed-off-by: Tomas Winkler
> > > Signed-off-by: Daniele Ceraolo Spurio
> > >
> > > Cc: Vitaly Lubart
> > > Cc: Greg Kroah-Hartman
> > > Reviewed-by: Alan Previn
> > > ---
> > > drivers/misc/mei/pxp/mei_pxp.c | 13 ++---
> > > 1 file changed, 10 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/misc/mei/pxp/mei_pxp.c
> > > b/drivers/misc/mei/pxp/mei_pxp.c index 17c5d201603f..afc047627800
> > > 100644
> > > --- a/drivers/misc/mei/pxp/mei_pxp.c
> > > +++ b/drivers/misc/mei/pxp/mei_pxp.c
> > > @@ -159,17 +159,24 @@ static int mei_pxp_component_match(struct
> > device
> > > *dev, int subcomponent, {
> > > struct device *base = data;
> > >
> > > + if (!dev)
> > > + return 0;
> >
> > How can that happen?
> >
> > > +
> > > if (!dev->driver || strcmp(dev->driver->name, "i915") ||
> >
> > That's crazy to assume, but whatever :(
> Explained here:
> https://lore.kernel.org/all/20220418175932.1809770-2-wonch...@google.com/
Still crazy :(
>
> >
> > > subcomponent != I915_COMPONENT_PXP)
> > > return 0;
> > >
> > > base = base->parent;
> > > - if (!base)
> > > + if (!base) /* mei device */
> >
> > Why does this mean that?
> >
> > Where is that documented?
> >
> > > return 0;
> > >
> > > - base = base->parent;
> > > - dev = dev->parent;
> > > + base = base->parent; /* pci device */
> >
> > Again, why is this the case?
> >
> > > + /* for dgfx */
> > > + if (base && dev == base)
> > > + return 1;
> > >
> > > + /* for pch */
> > > + dev = dev->parent;
> >
> > You are digging through a random device tree and assuming that you "know"
> > what the topology is going to be, that feels very very fragile and ripe for
> > problems going forward.
>
> I don't think it is random.
Today it is one specific way, but how do you know this always will be
this way?
> > How do you ensure that this really is they way the tree is for ALL systems?
>
> Yes we take the topology assumption in PCI hierarchy.
> There is a case where both GFX and MEI are in PCH and you cannot stick
> additional PCI extender or anything else there.
> And case where MEI is child on a standalone graphics card this is set in
> software so topology is not going to change unless we rewrite
> everything. Be happy to hear your insights.
This is ripe to break in the future if someone makes a differently
structured device as there is nothing forcing the current layout to
always be this way by hardware designers.
The goal of the driver model is to NOT have these types of hard-coded
topology assumptions because, supprise, assumptions like this have
always come back to bite people in the end.
This is your driver, so that's fine, but really this feels very very
wrong and you will have a hard time guaranteeing that this will always
be this way for the next 20+ years of hardware designs. So why not do
it properly from the beginning and pass in the correct pointers to
different places?
There is a very good reason that the driver model/core does not make it
easy to determine what type of device a 'struct device *' is, because
you shouldn't have to rely on that type of thing ever. You are taking
it one step further and just assuming that you know what the type is
here, with no real way to ensure that this is the case.
In short, this feels like a very bad design as it is very fragile.
thanks,
greg k-h
RE: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card
> -Original Message-
> From: Greg Kroah-Hartman
> Sent: Friday, September 09, 2022 09:16
> To: Ceraolo Spurio, Daniele
> Cc: intel-...@lists.freedesktop.org; dri-devel@lists.freedesktop.org;
> Winkler, Tomas ; Lubart, Vitaly
> ; Teres Alexis, Alan Previn
>
> Subject: Re: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete
> card
>
> On Thu, Sep 08, 2022 at 05:16:03PM -0700, Daniele Ceraolo Spurio wrote:
> > From: Tomas Winkler
> >
> > With on-boards graphics card, both i915 and MEI are in the same device
> > hierarchy with the same parent, while for discrete gfx card the MEI is
> > its child device.
> > Adjust the match function for that scenario by matching MEI parent
> > device with i915.
> >
> > V2:
> > 1. More detailed commit message
> > 2. Check for dev is not null before it is accessed.
> >
> > Signed-off-by: Tomas Winkler
> > Signed-off-by: Daniele Ceraolo Spurio
> >
> > Cc: Vitaly Lubart
> > Cc: Greg Kroah-Hartman
> > Reviewed-by: Alan Previn
> > ---
> > drivers/misc/mei/pxp/mei_pxp.c | 13 ++---
> > 1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/misc/mei/pxp/mei_pxp.c
> > b/drivers/misc/mei/pxp/mei_pxp.c index 17c5d201603f..afc047627800
> > 100644
> > --- a/drivers/misc/mei/pxp/mei_pxp.c
> > +++ b/drivers/misc/mei/pxp/mei_pxp.c
> > @@ -159,17 +159,24 @@ static int mei_pxp_component_match(struct
> device
> > *dev, int subcomponent, {
> > struct device *base = data;
> >
> > + if (!dev)
> > + return 0;
>
> How can that happen?
>
> > +
> > if (!dev->driver || strcmp(dev->driver->name, "i915") ||
>
> That's crazy to assume, but whatever :(
Explained here:
https://lore.kernel.org/all/20220418175932.1809770-2-wonch...@google.com/
>
> > subcomponent != I915_COMPONENT_PXP)
> > return 0;
> >
> > base = base->parent;
> > - if (!base)
> > + if (!base) /* mei device */
>
> Why does this mean that?
>
> Where is that documented?
>
> > return 0;
> >
> > - base = base->parent;
> > - dev = dev->parent;
> > + base = base->parent; /* pci device */
>
> Again, why is this the case?
>
> > + /* for dgfx */
> > + if (base && dev == base)
> > + return 1;
> >
> > + /* for pch */
> > + dev = dev->parent;
>
> You are digging through a random device tree and assuming that you "know"
> what the topology is going to be, that feels very very fragile and ripe for
> problems going forward.
I don't think it is random.
> How do you ensure that this really is they way the tree is for ALL systems?
Yes we take the topology assumption in PCI hierarchy.
There is a case where both GFX and MEI are in PCH and you cannot stick
additional PCI extender or anything else there.
And case where MEI is child on a standalone graphics card this is set in
software so topology is not going to change unless we rewrite
everything. Be happy to hear your insights.
Thanks
Tomas
Re: [PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card
On Thu, Sep 08, 2022 at 05:16:03PM -0700, Daniele Ceraolo Spurio wrote:
> From: Tomas Winkler
>
> With on-boards graphics card, both i915 and MEI
> are in the same device hierarchy with the same parent,
> while for discrete gfx card the MEI is its child device.
> Adjust the match function for that scenario
> by matching MEI parent device with i915.
>
> V2:
> 1. More detailed commit message
> 2. Check for dev is not null before it is accessed.
>
> Signed-off-by: Tomas Winkler
> Signed-off-by: Daniele Ceraolo Spurio
> Cc: Vitaly Lubart
> Cc: Greg Kroah-Hartman
> Reviewed-by: Alan Previn
> ---
> drivers/misc/mei/pxp/mei_pxp.c | 13 ++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/misc/mei/pxp/mei_pxp.c b/drivers/misc/mei/pxp/mei_pxp.c
> index 17c5d201603f..afc047627800 100644
> --- a/drivers/misc/mei/pxp/mei_pxp.c
> +++ b/drivers/misc/mei/pxp/mei_pxp.c
> @@ -159,17 +159,24 @@ static int mei_pxp_component_match(struct device *dev,
> int subcomponent,
> {
> struct device *base = data;
>
> + if (!dev)
> + return 0;
How can that happen?
> +
> if (!dev->driver || strcmp(dev->driver->name, "i915") ||
That's crazy to assume, but whatever :(
> subcomponent != I915_COMPONENT_PXP)
> return 0;
>
> base = base->parent;
> - if (!base)
> + if (!base) /* mei device */
Why does this mean that?
Where is that documented?
> return 0;
>
> - base = base->parent;
> - dev = dev->parent;
> + base = base->parent; /* pci device */
Again, why is this the case?
> + /* for dgfx */
> + if (base && dev == base)
> + return 1;
>
> + /* for pch */
> + dev = dev->parent;
You are digging through a random device tree and assuming that you
"know" what the topology is going to be, that feels very very fragile
and ripe for problems going forward.
How do you ensure that this really is they way the tree is for ALL
systems?
thanks,
greg k-h
[PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card
From: Tomas Winkler
With on-boards graphics card, both i915 and MEI
are in the same device hierarchy with the same parent,
while for discrete gfx card the MEI is its child device.
Adjust the match function for that scenario
by matching MEI parent device with i915.
V2:
1. More detailed commit message
2. Check for dev is not null before it is accessed.
Signed-off-by: Tomas Winkler
Signed-off-by: Daniele Ceraolo Spurio
Cc: Vitaly Lubart
Cc: Greg Kroah-Hartman
Reviewed-by: Alan Previn
---
drivers/misc/mei/pxp/mei_pxp.c | 13 ++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/mei/pxp/mei_pxp.c b/drivers/misc/mei/pxp/mei_pxp.c
index 17c5d201603f..afc047627800 100644
--- a/drivers/misc/mei/pxp/mei_pxp.c
+++ b/drivers/misc/mei/pxp/mei_pxp.c
@@ -159,17 +159,24 @@ static int mei_pxp_component_match(struct device *dev,
int subcomponent,
{
struct device *base = data;
+ if (!dev)
+ return 0;
+
if (!dev->driver || strcmp(dev->driver->name, "i915") ||
subcomponent != I915_COMPONENT_PXP)
return 0;
base = base->parent;
- if (!base)
+ if (!base) /* mei device */
return 0;
- base = base->parent;
- dev = dev->parent;
+ base = base->parent; /* pci device */
+ /* for dgfx */
+ if (base && dev == base)
+ return 1;
+ /* for pch */
+ dev = dev->parent;
return (base && dev && dev == base);
}
--
2.37.2
