linux-kernel - Re: [PATCH 01/13] drm/exynos: Stop using frame

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Date:   Wed, 7 Oct 2020 14:36:52 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
CC:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>, <linux-s390@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        "Jason Gunthorpe" <jgg@...pe.ca>, Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        "Kyungmin Park" <kyungmin.park@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        "Krzysztof Kozlowski" <krzk@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 01/13] drm/exynos: Stop using frame_vector helpers

On 10/7/20 2:32 PM, Daniel Vetter wrote:
> On Wed, Oct 7, 2020 at 10:33 PM John Hubbard <jhubbard@...dia.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