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

From: Benjamin Gaignard
Date: Tue Jan 30 2018 - 10:08:56 EST


2018-01-30 15:58 GMT+01:00 Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>:
> Hi Philippe,
>
> Thank you for the patch.
>
> 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@xxxxxx>
>> Signed-off-by: Vincent Abriou <vincent.abriou@xxxxxx>
>> Signed-off-by: Philippe Cornu <philippe.cornu@xxxxxx>
>> ---
>> 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

>
>> +}
>> +
>> 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
>