Re: [Intel-gfx] [PATCH 4/4] drm/i915: Move ioremap_wc tracking onto VMA
On Wed, Apr 20, 2016 at 11:27:27PM +0200, Luis R. Rodriguez wrote: > On Wed, Apr 20, 2016 at 01:17:30PM +0200, Daniel Vetter wrote: > > On Wed, Apr 20, 2016 at 11:10:54AM +0200, Luis R. Rodriguez wrote: > > > Reason I ask is since I noticed a while ago a lot of drivers > > > were using info->fix.smem_start and info->fix.smem_len consistently > > > for their ioremap'd areas it might make sense instead to let the > > > internal framebuffer (register_framebuffer()) optionally manage the > > > ioremap_wc() for drivers, given that this is pretty generic stuff. > > > > All that legacy fbdev stuff is just for legacy support, and I prefer to > > have that as dumb as possible. There's been some discussion even around > > lifting the "kick out firmware fb driver" out of fbdev, since we'd need it > > to have a simple drm driver for e.g. uefi. > > > > But I definitely don't want a legacy horror show like fbdev to > > automagically take care of device mappings for drivers. > > Makes sense, it also still begs the question if more modern APIs > could manage the ioremap for you. Evidence shows people get > sloppy and if things were done internally with helpers it may > be easier to later make adjustments. Real gpus generally have so much mmio space that you want to ioremap them on demand. At least if you still care about 32bit support. And on-die gpus on socs or similar tend to not have an mmio range to access the gfx remapping range at all, but instead expect that to be done with gpu pagetables. So at least with gpus I don't see a real demand for this, and the existing users are mostly old fbdev drivers that really no one should be touching ;-) Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
Re: [Intel-gfx] [PATCH 4/4] drm/i915: Move ioremap_wc tracking onto VMA
On Wed, Apr 20, 2016 at 01:17:30PM +0200, Daniel Vetter wrote: > On Wed, Apr 20, 2016 at 11:10:54AM +0200, Luis R. Rodriguez wrote: > > Reason I ask is since I noticed a while ago a lot of drivers > > were using info->fix.smem_start and info->fix.smem_len consistently > > for their ioremap'd areas it might make sense instead to let the > > internal framebuffer (register_framebuffer()) optionally manage the > > ioremap_wc() for drivers, given that this is pretty generic stuff. > > All that legacy fbdev stuff is just for legacy support, and I prefer to > have that as dumb as possible. There's been some discussion even around > lifting the "kick out firmware fb driver" out of fbdev, since we'd need it > to have a simple drm driver for e.g. uefi. > > But I definitely don't want a legacy horror show like fbdev to > automagically take care of device mappings for drivers. Makes sense, it also still begs the question if more modern APIs could manage the ioremap for you. Evidence shows people get sloppy and if things were done internally with helpers it may be easier to later make adjustments. Luis
Re: [Intel-gfx] [PATCH 4/4] drm/i915: Move ioremap_wc tracking onto VMA
On Wed, Apr 20, 2016 at 11:10:54AM +0200, Luis R. Rodriguez wrote: > Reason I ask is since I noticed a while ago a lot of drivers > were using info->fix.smem_start and info->fix.smem_len consistently > for their ioremap'd areas it might make sense instead to let the > internal framebuffer (register_framebuffer()) optionally manage the > ioremap_wc() for drivers, given that this is pretty generic stuff. All that legacy fbdev stuff is just for legacy support, and I prefer to have that as dumb as possible. There's been some discussion even around lifting the "kick out firmware fb driver" out of fbdev, since we'd need it to have a simple drm driver for e.g. uefi. But I definitely don't want a legacy horror show like fbdev to automagically take care of device mappings for drivers. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
Re: [PATCH 4/4] drm/i915: Move ioremap_wc tracking onto VMA
On Wed, Apr 20, 2016 at 11:10:54AM +0200, Luis R. Rodriguez wrote:
> On Tue, Apr 19, 2016 at 01:33:58PM +0100, Chris Wilson wrote:
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c
> > b/drivers/gpu/drm/i915/i915_gem.c
> > index 6ce2c31b9a81..9ef47329e8ae 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -3346,6 +3346,15 @@ static void i915_gem_object_finish_gtt(struct
> > drm_i915_gem_object *obj)
> > old_write_domain);
> > }
> >
> > +static void __i915_vma_iounmap(struct i915_vma *vma)
> > +{
> > + if (vma->iomap == NULL)
> > + return;
> > +
> > + io_mapping_unmap(vma->iomap);
>
> The NULL check could just be done by io_mapping_unmap() then you
> can avoid this in other drivers too.
>
> > + vma->iomap = NULL;
>
> You added accounting here, by simple int and inc / dec'ing it.
> I cannot confirm if it is correctly avoiding races, can you
> confirm?
Yes, the vma->pin_count is guarded by the struct_mutex atm. (The
struct_mutex is our own BKL :(
> Also you added accounting for the custom vma pinning thing and do
> GEM_BUG_ON(vma->pin_count == 0); when you unpin one instance but *you do not*
> do something like GEM_BUG_ON(vma->pin_count != 0); when you do the final full
> iounmap. That seems rather sloppy.
It's placed next to the function where pin_count == 0 and only called
from it. Yes, I did think the same...
> iomapping stuff has its own custom data structure, why not just use that data
> structure instead of the struct i915_vma and generalize this ? Drivers can
> be buggy and best if we avoid custom driver accounting and just do it in a
> neat
> generic fashion.
Completely different tasks, as far as I am aware. The iomapping is about
providing CPU access to the IO region, dma-remapping about providing
device access to physical memory, and our own VMA is about how the
object sits in all the different views of both CPU and device address
spaces (of which there are many, and even the CPU accessible address
space is not the entirety of that particular address space).
> Then other drivers could use this too.
drivers/gpu/drm/ttm (you didn't hear me say that...)
> > diff --git a/drivers/gpu/drm/i915/intel_fbdev.c
> > b/drivers/gpu/drm/i915/intel_fbdev.c
> > index 79ac202f3870..93f54a10042f 100644
> > --- a/drivers/gpu/drm/i915/intel_fbdev.c
> > +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> > @@ -244,22 +245,23 @@ static int intelfb_create(struct drm_fb_helper
> > *helper,
> > info->flags = FBINFO_DEFAULT | FBINFO_CAN_FORCE_OUTPUT;
> > info->fbops = _ops;
> >
> > + vma = i915_gem_obj_to_ggtt(obj);
> > +
> > /* setup aperture base/size for vesafb takeover */
> > info->apertures->ranges[0].base = dev->mode_config.fb_base;
> > info->apertures->ranges[0].size = ggtt->mappable_end;
> >
> > - info->fix.smem_start = dev->mode_config.fb_base +
> > i915_gem_obj_ggtt_offset(obj);
> > - info->fix.smem_len = size;
> > + info->fix.smem_start = dev->mode_config.fb_base + vma->node.start;
> > + info->fix.smem_len = vma->node.size;
> >
> > - info->screen_base =
> > - ioremap_wc(ggtt->mappable_base + i915_gem_obj_ggtt_offset(obj),
> > - size);
> > - if (!info->screen_base) {
> > + vaddr = i915_vma_pin_iomap(vma);
> > + if (IS_ERR(vaddr)) {
> > DRM_ERROR("Failed to remap framebuffer into virtual memory\n");
> > - ret = -ENOSPC;
> > + ret = PTR_ERR(vaddr);
> > goto out_destroy_fbi;
> > }
> > - info->screen_size = size;
> > + info->screen_base = vaddr;
> > + info->screen_size = vma->node.size;
>
> some framebuffer drivers tend to use a generic start address of
> iinfo->fix.smem_start and a length of info->fix.smem_len, this
> driver sets the smem_start above, but its different than what
> gets ioremap for a start address:
>
> + ptr = io_mapping_map_wc(i915_vm_to_ggtt(vma->vm)->mappable,
> + vma->node.start,
> + vma->node.size);
>
> fix.smem_start is :
>
>
> > + info->fix.smem_start = dev->mode_config.fb_base + vma->node.start;
>
> The smem_len matches though. Can you clarify if its correct for
> the io_mapping_map_wc() should not be using info->fix.smem_start
> (which is dev->mode_config.fb_base + vma->node.start)?
dev->mode_config.fb_base is the base address of the mappable region. It
is an inconsistently in naming that just hasn't annoyed me enough to
fix.
> Reason I ask is since I noticed a while ago a lot of drivers
> were using info->fix.smem_start and info->fix.smem_len consistently
> for their ioremap'd areas it might make sense instead to let the
> internal framebuffer (register_framebuffer()) optionally manage the
> ioremap_wc() for drivers, given that this is pretty generic stuff.
Apart from drivers like ours we would end up with multiple mappings to
the same region. It was
Re: [PATCH 4/4] drm/i915: Move ioremap_wc tracking onto VMA
On Tue, Apr 19, 2016 at 01:33:58PM +0100, Chris Wilson wrote:
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 6ce2c31b9a81..9ef47329e8ae 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3346,6 +3346,15 @@ static void i915_gem_object_finish_gtt(struct
> drm_i915_gem_object *obj)
> old_write_domain);
> }
>
> +static void __i915_vma_iounmap(struct i915_vma *vma)
> +{
> + if (vma->iomap == NULL)
> + return;
> +
> + io_mapping_unmap(vma->iomap);
The NULL check could just be done by io_mapping_unmap() then you
can avoid this in other drivers too.
> + vma->iomap = NULL;
You added accounting here, by simple int and inc / dec'ing it.
I cannot confirm if it is correctly avoiding races, can you
confirm?
Also you added accounting for the custom vma pinning thing and do
GEM_BUG_ON(vma->pin_count == 0); when you unpin one instance but *you do not*
do something like GEM_BUG_ON(vma->pin_count != 0); when you do the final full
iounmap. That seems rather sloppy.
iomapping stuff has its own custom data structure, why not just use that data
structure instead of the struct i915_vma and generalize this ? Drivers can
be buggy and best if we avoid custom driver accounting and just do it in a neat
generic fashion.
Then other drivers could use this too.
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c
> b/drivers/gpu/drm/i915/intel_fbdev.c
> index 79ac202f3870..93f54a10042f 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -244,22 +245,23 @@ static int intelfb_create(struct drm_fb_helper *helper,
> info->flags = FBINFO_DEFAULT | FBINFO_CAN_FORCE_OUTPUT;
> info->fbops = _ops;
>
> + vma = i915_gem_obj_to_ggtt(obj);
> +
> /* setup aperture base/size for vesafb takeover */
> info->apertures->ranges[0].base = dev->mode_config.fb_base;
> info->apertures->ranges[0].size = ggtt->mappable_end;
>
> - info->fix.smem_start = dev->mode_config.fb_base +
> i915_gem_obj_ggtt_offset(obj);
> - info->fix.smem_len = size;
> + info->fix.smem_start = dev->mode_config.fb_base + vma->node.start;
> + info->fix.smem_len = vma->node.size;
>
> - info->screen_base =
> - ioremap_wc(ggtt->mappable_base + i915_gem_obj_ggtt_offset(obj),
> -size);
> - if (!info->screen_base) {
> + vaddr = i915_vma_pin_iomap(vma);
> + if (IS_ERR(vaddr)) {
> DRM_ERROR("Failed to remap framebuffer into virtual memory\n");
> - ret = -ENOSPC;
> + ret = PTR_ERR(vaddr);
> goto out_destroy_fbi;
> }
> - info->screen_size = size;
> + info->screen_base = vaddr;
> + info->screen_size = vma->node.size;
some framebuffer drivers tend to use a generic start address of
iinfo->fix.smem_start and a length of info->fix.smem_len, this
driver sets the smem_start above, but its different than what
gets ioremap for a start address:
+ ptr = io_mapping_map_wc(i915_vm_to_ggtt(vma->vm)->mappable,
+ vma->node.start,
+ vma->node.size);
fix.smem_start is :
> + info->fix.smem_start = dev->mode_config.fb_base + vma->node.start;
The smem_len matches though. Can you clarify if its correct for
the io_mapping_map_wc() should not be using info->fix.smem_start
(which is dev->mode_config.fb_base + vma->node.start)?
Reason I ask is since I noticed a while ago a lot of drivers
were using info->fix.smem_start and info->fix.smem_len consistently
for their ioremap'd areas it might make sense instead to let the
internal framebuffer (register_framebuffer()) optionally manage the
ioremap_wc() for drivers, given that this is pretty generic stuff.
Luis
