[PATCH] drm: modify pages_to_sg prime helper to create optimized SG table

[Rahul Sharma]

On Tue, Jan 29, 2013 at 10:40 PM, Aaron Plattner <aplattner at nvidia.com> wrote:
> On 01/28/2013 05:38 AM, Rahul Sharma wrote:
>>
>> It fixes the issue arises due to passing 'nr_pages' in place of 'nents' to
>> sg_alloc_table. When ARM_HAS_SG_CHAIN is disabled, it is causing failure
>> in
>> creating SG table for the buffers having more than 204 physical pages i.e.
>> equal to SG_MAX_SINGLE_ALLOC.
>>
>> When using sg_alloc_table_from_pages interface, in place of
>> sg_alloc_table,
>> page list will be passes to get each contiguous section which is
>> represented
>> by a single entry in the table. For a Contiguous Buffer, number of entries
>> should be equal to 1.
>>
>> Following check is causing the failure which is not applicable for
>> Non-Contig
>> buffers:
>>
>>         if (WARN_ON_ONCE(nents > max_ents))
>>                 return -EINVAL;
>>
>> Above patch is well tested for EXYNOS4 and EXYNOS5 for with/wihtout IOMMU
>> supprot. NOUVEAU and RADEON platforms also depends on
>> drm_prime_pages_to_sg
>> helper function.
>>
>> This set is base on "exynos-drm-fixes" branch at
>> http://git.kernel.org/?p=linux/kernel/git/daeinki/drm-exynos.git
>>
>> Signed-off-by: Rahul Sharma <rahul.sharma at samsung.com>
>
>
> Reviewed-by: Aaron Plattner <aplattner at nvidia.com>
>
> I also verified that this reduces my 2025-entry sg_table to 6 entries, so
>
> Tested-by: Aaron Plattner <aplattner at nvidia.com>
>
> --
> Aaron
>

Thanks Aaron,

I want to request stake-holders to review and test this patch for
other platforms.

regards,
Rahul Sharma.

>
>> ---
>>   drivers/gpu/drm/drm_prime.c | 8 ++------
>>   1 file changed, 2 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
>> index 7f12573..072ee08 100644
>> --- a/drivers/gpu/drm/drm_prime.c
>> +++ b/drivers/gpu/drm/drm_prime.c
>> @@ -217,21 +217,17 @@ int drm_prime_fd_to_handle_ioctl(struct drm_device
>> *dev, void *data,
>>   struct sg_table *drm_prime_pages_to_sg(struct page **pages, int
>> nr_pages)
>>   {
>>         struct sg_table *sg = NULL;
>> -       struct scatterlist *iter;
>> -       int i;
>>         int ret;
>>
>>         sg = kmalloc(sizeof(struct sg_table), GFP_KERNEL);
>>         if (!sg)
>>                 goto out;
>>
>> -       ret = sg_alloc_table(sg, nr_pages, GFP_KERNEL);
>> +       ret = sg_alloc_table_from_pages(sg, pages, nr_pages, 0,
>> +                               nr_pages << PAGE_SHIFT, GFP_KERNEL);
>>         if (ret)
>>                 goto out;
>>
>> -       for_each_sg(sg->sgl, iter, nr_pages, i)
>> -               sg_set_page(iter, pages[i], PAGE_SIZE, 0);
>> -
>>         return sg;
>>   out:
>>         kfree(sg);
>>
>
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