[PATCH 1/4] drm/vram: Add helpers to validate a display mode's memory requirements
Daniel Vetter
daniel at ffwll.ch
Mon Feb 3 09:53:06 UTC 2020
On Mon, Feb 03, 2020 at 10:49:30AM +0100, Daniel Vetter wrote:
> On Sat, Feb 01, 2020 at 01:27:41PM +0100, Thomas Zimmermann wrote:
> > Devices with low amount of dedicated video memory may not be able
> > to use all possible display modes, as the framebuffers may not fit
> > into VRAM. The new helper function drm_vram_helper_mode_valid()
> > implements a simple test to sort out all display modes that can
> > not be used in any case. Drivers should call this function from
> > struct drm_mode_config_funcs.mode_valid.
> >
> > Calling drm_vram_helper_mode_valid() works best for 32-bit framebuffers;
> > drivers with framebuffers of different color depth can use
> > drm_vram_helper_mode_valid_internal() instead.
> >
> > The functionality was originally implemented by the ast driver, which
> > is being converted as well.
> >
> > Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> > ---
> > drivers/gpu/drm/ast/ast_main.c | 24 +--------
> > drivers/gpu/drm/drm_gem_vram_helper.c | 76 +++++++++++++++++++++++++++
> > include/drm/drm_gem_vram_helper.h | 14 +++++
> > 3 files changed, 91 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
> > index b79f484e9bd2..18a0a4ce00f6 100644
> > --- a/drivers/gpu/drm/ast/ast_main.c
> > +++ b/drivers/gpu/drm/ast/ast_main.c
> > @@ -388,31 +388,9 @@ static int ast_get_dram_info(struct drm_device *dev)
> > return 0;
> > }
> >
> > -enum drm_mode_status ast_mode_config_mode_valid(struct drm_device *dev,
> > - const struct drm_display_mode *mode)
> > -{
> > - static const unsigned long max_bpp = 4; /* DRM_FORMAT_XRGBA8888 */
> > -
> > - struct ast_private *ast = dev->dev_private;
> > - unsigned long fbsize, fbpages, max_fbpages;
> > -
> > - /* To support double buffering, a framebuffer may not
> > - * consume more than half of the available VRAM.
> > - */
> > - max_fbpages = (ast->vram_size / 2) >> PAGE_SHIFT;
> > -
> > - fbsize = mode->hdisplay * mode->vdisplay * max_bpp;
> > - fbpages = DIV_ROUND_UP(fbsize, PAGE_SIZE);
> > -
> > - if (fbpages > max_fbpages)
> > - return MODE_MEM;
> > -
> > - return MODE_OK;
> > -}
> > -
> > static const struct drm_mode_config_funcs ast_mode_funcs = {
> > .fb_create = drm_gem_fb_create,
> > - .mode_valid = ast_mode_config_mode_valid,
> > + .mode_valid = drm_vram_helper_mode_valid,
> > .atomic_check = drm_atomic_helper_check,
> > .atomic_commit = drm_atomic_helper_commit,
> > };
> > diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
> > index a4863326061a..89aebd500655 100644
> > --- a/drivers/gpu/drm/drm_gem_vram_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
> > @@ -1141,3 +1141,79 @@ void drm_vram_helper_release_mm(struct drm_device *dev)
> > dev->vram_mm = NULL;
> > }
> > EXPORT_SYMBOL(drm_vram_helper_release_mm);
> > +
> > +/*
> > + * Mode-config helpers
> > + */
> > +
> > +/**
> > + * drm_vram_helper_mode_valid_internal - Tests if a display mode's
> > + * framebuffer fits into the available video memory.
> > + * @dev: the DRM device
> > + * @mode: the mode to test
> > + * @max_bpp: the maximum number of bytes per pixel
>
> Does this render correctly? I thought an empty comment line is required
> between comments and the free-form paragraphs ... Also usual style (in drm
> at least) is that the Returns: block is more towards the end of the text,
> and not indented.
>
>
> > + * Returns:
> > + * MODE_OK the display mode is supported, or an error code of type
> > + * enum drm_mode_status otherwise.
> > + *
> > + * This function tests if enough video memory is available using the
> > + * specified display mode. Atomic modesetting requires importing the
> > + * designated framebuffer into video memory before evicting the active
> > + * one. Hence, any framebuffer may consume at most half of the available
> > + * VRAM. Display modes that require a larger framebuffer can not be used,
> > + * even of the CRTC does support them.
> > + *
> > + * Drivers should call this function from
> > + * struct drm_mode_config_funcs.mode_valid. See drm_vram_helper_mode_valid()
> > + * for framebuffers that use at most 32-bit color depth.
> > + *
> > + * Note:
> > + * The function can only test if the display mode is supported in
> > + * general. If you have too many framebuffers pinned to video memory,
> > + * a display mode may still not be usable in practice.
> > + */
> > +enum drm_mode_status
> > +drm_vram_helper_mode_valid_internal(struct drm_device *dev,
> > + const struct drm_display_mode *mode,
> > + unsigned long max_bpp)
> > +{
> > + struct drm_vram_mm *vmm = dev->vram_mm;
> > + unsigned long fbsize, fbpages, max_fbpages;
> > +
> > + if (!dev->vram_mm)
>
> This is a driver bug imo (most likely of enabling hotplug/output detection
> before the vram handling is set up), needs to be wrapped in a WARN_ON to
> catch this.
>
> > + return MODE_BAD;
> > +
> > + max_fbpages = (vmm->vram_size / 2) >> PAGE_SHIFT;
> > +
> > + fbsize = mode->hdisplay * mode->vdisplay * max_bpp;
> > + fbpages = DIV_ROUND_UP(fbsize, PAGE_SIZE);
> > +
> > + if (fbpages > max_fbpages)
> > + return MODE_MEM;
> > +
> > + return MODE_OK;
> > +}
> > +EXPORT_SYMBOL(drm_vram_helper_mode_valid_internal);
>
> Anyway, patch looks good (with the nits addressed one way or the other):
>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> > +
> > +/**
> > + * drm_vram_helper_mode_valid - Tests if a display mode's
> > + * framebuffer fits into the available video memory.
> > + * @dev: the DRM device
> > + * @mode: the mode to test
> > + * Returns:
> > + * MODE_OK the display mode is supported, or an error code of type
> > + * enum drm_mode_status otherwise.
> > + *
> > + * This function is a variant of drm_vram_helper_mode_valid_internal()
> > + * for framebuffers that use at most 32-bit color depth. It can be plugged
> > + * directly into struct drm_mode_config_funcs.mode_valid.
> > + */
> > +enum drm_mode_status
> > +drm_vram_helper_mode_valid(struct drm_device *dev,
> > + const struct drm_display_mode *mode)
> > +{
> > + static const unsigned long max_bpp = 4; /* DRM_FORMAT_XRGBA8888 */
> > +
> > + return drm_vram_helper_mode_valid_internal(dev, mode, max_bpp);
Since you don't use the _internal() version anywhere yet ... What about
unexporting that and instead using the preferred_bpp setting to compute
valid modes? I suspect that should dtrt almost anywhere ...
-Daniel
> > +}
> > +EXPORT_SYMBOL(drm_vram_helper_mode_valid);
> > diff --git a/include/drm/drm_gem_vram_helper.h b/include/drm/drm_gem_vram_helper.h
> > index 573e9fd109bf..e7d9144c79ad 100644
> > --- a/include/drm/drm_gem_vram_helper.h
> > +++ b/include/drm/drm_gem_vram_helper.h
> > @@ -6,6 +6,7 @@
> > #include <drm/drm_file.h>
> > #include <drm/drm_gem.h>
> > #include <drm/drm_ioctl.h>
> > +#include <drm/drm_modes.h>
> > #include <drm/ttm/ttm_bo_api.h>
> > #include <drm/ttm/ttm_bo_driver.h>
> > #include <drm/ttm/ttm_placement.h>
> > @@ -205,4 +206,17 @@ struct drm_vram_mm *drm_vram_helper_alloc_mm(
> > struct drm_device *dev, uint64_t vram_base, size_t vram_size);
> > void drm_vram_helper_release_mm(struct drm_device *dev);
> >
> > +/*
> > + * Mode-config helpers
> > + */
> > +
> > +enum drm_mode_status
> > +drm_vram_helper_mode_valid_internal(struct drm_device *dev,
> > + const struct drm_display_mode *mode,
> > + unsigned long max_bpp);
> > +
> > +enum drm_mode_status
> > +drm_vram_helper_mode_valid(struct drm_device *dev,
> > + const struct drm_display_mode *mode);
> > +
> > #endif
> > --
> > 2.25.0
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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