linux-kernel - Re: [PATCH v2] drm/stm: drv: Improve data transfers

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Message-ID: <28099300.xC2jyNz3X5@avalon>
Date:   Tue, 30 Jan 2018 17:10:43 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Benjamin Gaignard <benjamin.gaignard@...aro.org>
Cc:     Philippe Cornu <philippe.cornu@...com>,
        Yannick Fertre <yannick.fertre@...com>,
        Vincent Abriou <vincent.abriou@...com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Fabien Dessenne <fabien.dessenne@...com>,
        Mickael Reulier <mickael.reulier@...com>,
        Ludovic Barre <ludovic.barre@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>
Subject: Re: [PATCH v2] drm/stm: drv: Improve data transfers

Hi Benjamin,

On Tuesday, 30 January 2018 17:08:48 EET Benjamin Gaignard wrote:
> 2018-01-30 15:58 GMT+01:00 Laurent Pinchart:
> > On Tuesday, 30 January 2018 12:42:00 EET Philippe Cornu wrote:
> >> To optimize data transfers, align pitch on 128 bytes & height
> >> on 4 bytes. This optimization is not applicable on hw without MMU.
> >> 
> >> Signed-off-by: Yannick Fertre <yannick.fertre@...com>
> >> Signed-off-by: Vincent Abriou <vincent.abriou@...com>
> >> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
> >> ---
> >> Changes in v2: Rename stm_dumb_create() to stm_gem_cma_dumb_create() and
> >> 
> >>   move CONFIG_MMU inside the function following comments from Benjamin
> >>   Gaignard.
> >>  
> >>  drivers/gpu/drm/stm/drv.c | 20 +++++++++++++++++++-
> >>  1 file changed, 19 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/gpu/drm/stm/drv.c b/drivers/gpu/drm/stm/drv.c
> >> index 8fe954c27fba..8bc7e8418b8d 100644
> >> --- a/drivers/gpu/drm/stm/drv.c
> >> +++ b/drivers/gpu/drm/stm/drv.c
> >> @@ -31,6 +31,24 @@ static const struct drm_mode_config_funcs
> >> drv_mode_config_funcs = { .atomic_commit = drm_atomic_helper_commit,
> >> 
> >>  };
> >> 
> >> +static int stm_gem_cma_dumb_create(struct drm_file *file,
> >> +                                struct drm_device *dev,
> >> +                                struct drm_mode_create_dumb *args)
> >> +{
> >> +#ifdef CONFIG_MMU
> >> +     unsigned int min_pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
> >> +
> >> +     /*
> >> +      * in order to optimize data transfer, pitch is aligned on
> >> +      * 128 bytes, height is aligned on 4 bytes
> >> +      */
> >> +     args->pitch = roundup(min_pitch, 128);
> >> +     args->height = roundup(args->height, 4);
> >> +#endif
> >> +
> >> +     return drm_gem_cma_dumb_create_internal(file, dev, args);
> > 
> > In the !CONFIG_MMU case you now bypass the pitch and size calculations
> > performed by drm_gem_cma_dumb_create(), allowing userspace to allocate
> > arbitrarily large buffers. Is that intentional ?
> 
> My bad, I will send a fix

Thank you.

> >> +}
> >> +
> >> 
> >>  DEFINE_DRM_GEM_CMA_FOPS(drv_driver_fops);
> >>  
> >>  static struct drm_driver drv_driver = {
> >> 
> >> @@ -44,7 +62,7 @@ static struct drm_driver drv_driver = {
> >> 
> >>       .minor = 0,
> >>       .patchlevel = 0,
> >>       .fops = &drv_driver_fops,
> >> 
> >> -     .dumb_create = drm_gem_cma_dumb_create,
> >> +     .dumb_create = stm_gem_cma_dumb_create,
> >> 
> >>       .prime_handle_to_fd = drm_gem_prime_handle_to_fd,
> >>       .prime_fd_to_handle = drm_gem_prime_fd_to_handle,
> >>       .gem_free_object_unlocked = drm_gem_cma_free_object,

-- 
Regards,

Laurent Pinchart