Re: [Intel-gfx] [PATCH 3/5] drm/dp: Implement I2C_M_STOP for i2c-over-aux
On Wed, Dec 12, 2018 at 11:30:30AM +0100, Daniel Vetter wrote:
> On Mon, Dec 10, 2018 at 06:47:00PM -0800, Dhinakaran Pandiyan wrote:
> > On Fri, 2018-09-28 at 21:04 +0300, Ville Syrjala wrote:
> > > From: Ville Syrjälä
> > >
> > > Consult the I2C_M_STOP flag to determine whether to set the MOT bit
> > > or
> > > not. Makes it possible to send multiple messages in one go with
> > > stop+start generated between the messages (as opposed nothing or
> > > repstart depending on whether thr address/rw changed).
> > >
> > > Not sure anyone has actual use for this but figured I'd handle it
> > > since I started to look at that flag for MST remote i2c xfers.
> > >
> > Don't see the I2C_M_STOP flag anywhere in drm_edid.c, but the change
> > introduced here does make sense.
>
> Iirc it's the i2c core library which takes an entire transaction, splits
> it up, and sets the stop flag only on the very last one. Or something like
> that.
The last msg of the transfer has an implicit stop even without
the flag. The core won't add the flag for you. So the flag
is purely meant to force a stop+start between two messages
of the same transfer.
Well, it's not really specific anywhere IIRC but that's how
i2c-algo-bit behaves, and I tend to think of that one as the
defacto specification.
> -Daniel
>
> >
> > Reviewed-by: Dhinakaran Pandiyan
> > > Signed-off-by: Ville Syrjälä
> > > ---
> > > drivers/gpu/drm/drm_dp_helper.c | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > > b/drivers/gpu/drm/drm_dp_helper.c
> > > index 37c01b6076ec..e85cea299d2a 100644
> > > --- a/drivers/gpu/drm/drm_dp_helper.c
> > > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > > @@ -884,7 +884,8 @@ static void drm_dp_i2c_msg_set_request(struct
> > > drm_dp_aux_msg *msg,
> > > {
> > > msg->request = (i2c_msg->flags & I2C_M_RD) ?
> > > DP_AUX_I2C_READ : DP_AUX_I2C_WRITE;
> > > - msg->request |= DP_AUX_I2C_MOT;
> > > + if (!(i2c_msg->flags & I2C_M_STOP))
> > > + msg->request |= DP_AUX_I2C_MOT;
> > > }
> > >
> > > /*
> >
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> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
--
Ville Syrjälä
Intel
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Re: [Intel-gfx] [PATCH 3/5] drm/dp: Implement I2C_M_STOP for i2c-over-aux
On Mon, Dec 10, 2018 at 06:47:00PM -0800, Dhinakaran Pandiyan wrote:
> On Fri, 2018-09-28 at 21:04 +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä
> >
> > Consult the I2C_M_STOP flag to determine whether to set the MOT bit
> > or
> > not. Makes it possible to send multiple messages in one go with
> > stop+start generated between the messages (as opposed nothing or
> > repstart depending on whether thr address/rw changed).
> >
> > Not sure anyone has actual use for this but figured I'd handle it
> > since I started to look at that flag for MST remote i2c xfers.
> >
> Don't see the I2C_M_STOP flag anywhere in drm_edid.c, but the change
> introduced here does make sense.
Iirc it's the i2c core library which takes an entire transaction, splits
it up, and sets the stop flag only on the very last one. Or something like
that.
-Daniel
>
> Reviewed-by: Dhinakaran Pandiyan
> > Signed-off-by: Ville Syrjälä
> > ---
> > drivers/gpu/drm/drm_dp_helper.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > b/drivers/gpu/drm/drm_dp_helper.c
> > index 37c01b6076ec..e85cea299d2a 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -884,7 +884,8 @@ static void drm_dp_i2c_msg_set_request(struct
> > drm_dp_aux_msg *msg,
> > {
> > msg->request = (i2c_msg->flags & I2C_M_RD) ?
> > DP_AUX_I2C_READ : DP_AUX_I2C_WRITE;
> > - msg->request |= DP_AUX_I2C_MOT;
> > + if (!(i2c_msg->flags & I2C_M_STOP))
> > + msg->request |= DP_AUX_I2C_MOT;
> > }
> >
> > /*
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [Intel-gfx] [PATCH 3/5] drm/dp: Implement I2C_M_STOP for i2c-over-aux
On Fri, 2018-09-28 at 21:04 +0300, Ville Syrjala wrote:
> From: Ville Syrjälä
>
> Consult the I2C_M_STOP flag to determine whether to set the MOT bit
> or
> not. Makes it possible to send multiple messages in one go with
> stop+start generated between the messages (as opposed nothing or
> repstart depending on whether thr address/rw changed).
>
> Not sure anyone has actual use for this but figured I'd handle it
> since I started to look at that flag for MST remote i2c xfers.
>
Don't see the I2C_M_STOP flag anywhere in drm_edid.c, but the change
introduced here does make sense.
Reviewed-by: Dhinakaran Pandiyan
> Signed-off-by: Ville Syrjälä
> ---
> drivers/gpu/drm/drm_dp_helper.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c
> b/drivers/gpu/drm/drm_dp_helper.c
> index 37c01b6076ec..e85cea299d2a 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -884,7 +884,8 @@ static void drm_dp_i2c_msg_set_request(struct
> drm_dp_aux_msg *msg,
> {
> msg->request = (i2c_msg->flags & I2C_M_RD) ?
> DP_AUX_I2C_READ : DP_AUX_I2C_WRITE;
> - msg->request |= DP_AUX_I2C_MOT;
> + if (!(i2c_msg->flags & I2C_M_STOP))
> + msg->request |= DP_AUX_I2C_MOT;
> }
>
> /*
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[Intel-gfx] [PATCH 3/5] drm/dp: Implement I2C_M_STOP for i2c-over-aux
From: Ville Syrjälä
Consult the I2C_M_STOP flag to determine whether to set the MOT bit or
not. Makes it possible to send multiple messages in one go with
stop+start generated between the messages (as opposed nothing or
repstart depending on whether thr address/rw changed).
Not sure anyone has actual use for this but figured I'd handle it
since I started to look at that flag for MST remote i2c xfers.
Signed-off-by: Ville Syrjälä
---
drivers/gpu/drm/drm_dp_helper.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 37c01b6076ec..e85cea299d2a 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -884,7 +884,8 @@ static void drm_dp_i2c_msg_set_request(struct
drm_dp_aux_msg *msg,
{
msg->request = (i2c_msg->flags & I2C_M_RD) ?
DP_AUX_I2C_READ : DP_AUX_I2C_WRITE;
- msg->request |= DP_AUX_I2C_MOT;
+ if (!(i2c_msg->flags & I2C_M_STOP))
+ msg->request |= DP_AUX_I2C_MOT;
}
/*
--
2.16.4
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