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

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Date:   Tue, 30 Jan 2018 16:08:48 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
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

2018-01-30 15:58 GMT+01:00 Laurent Pinchart <laurent.pinchart@...asonboard.com>:
> 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@...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

>
>> +}
>> +
>>  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
>