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Subject: Re: [PATCH 01/13] drm/exynos: Stop using frame_vector helpers
To: Daniel Vetter <daniel.vetter@ffwll.ch>
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From: John Hubbard <jhubbard@nvidia.com>
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On 10/7/20 2:32 PM, Daniel Vetter wrote:
> On Wed, Oct 7, 2020 at 10:33 PM John Hubbard <jhubbard@nvidia.com> wrote:
>>
>> On 10/7/20 9:44 AM, Daniel Vetter wrote:
...
>>> @@ -398,15 +399,11 @@ static void g2d_userptr_put_dma_addr(struct g2d_data *g2d,
>>>        dma_unmap_sgtable(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt,
>>>                          DMA_BIDIRECTIONAL, 0);
>>>
>>> -     pages = frame_vector_pages(g2d_userptr->vec);
>>> -     if (!IS_ERR(pages)) {
>>> -             int i;
>>> +     for (i = 0; i < g2d_userptr->npages; i++)
>>> +             set_page_dirty_lock(g2d_userptr->pages[i]);
>>>
>>> -             for (i = 0; i < frame_vector_count(g2d_userptr->vec); i++)
>>> -                     set_page_dirty_lock(pages[i]);
>>> -     }
>>> -     put_vaddr_frames(g2d_userptr->vec);
>>> -     frame_vector_destroy(g2d_userptr->vec);
>>> +     unpin_user_pages(g2d_userptr->pages, g2d_userptr->npages);
>>> +     kvfree(g2d_userptr->pages);
>>
>> You can avoid writing your own loop, and just simplify the whole thing down to
>> two lines:
>>
>>          unpin_user_pages_dirty_lock(g2d_userptr->pages, g2d_userptr->npages,
>>                                      true);
>>          kvfree(g2d_userptr->pages);
> 
> Oh nice, this is neat. I'll also roll it out in the habanalabs patch,
> that has the same thing. Well almost, it only uses set_page_dirty, not
> the _lock variant. But I have no idea whether that matters or not?


It matters. And invariably, call sites that use set_page_dirty() instead
of set_page_dirty_lock() were already wrong.  Which is why I never had to
provide anything like "unpin_user_pages_dirty (not locked)".

Although in habanalabs case, I just reviewed patch 3 and I think they *were*
correctly using set_page_dirty_lock()...

thanks,
-- 
John Hubbard
NVIDIA