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Tue, 5 Oct 2021 08:16:11 +0000 Subject: Re: [PATCH 09/28] dma-buf: use the new iterator in dma_resv_poll To: Tvrtko Ursulin , linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, intel-gfx@lists.freedesktop.org Cc: daniel@ffwll.ch References: <20211001100610.2899-1-christian.koenig@amd.com> <20211001100610.2899-10-christian.koenig@amd.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: Date: Tue, 5 Oct 2021 10:16:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-ClientProxiedBy: AM0PR05CA0081.eurprd05.prod.outlook.com (2603:10a6:208:136::21) To MWHPR1201MB0192.namprd12.prod.outlook.com (2603:10b6:301:5a::14) MIME-Version: 1.0 Received: from [172.31.55.180] (165.204.72.6) by AM0PR05CA0081.eurprd05.prod.outlook.com (2603:10a6:208:136::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4566.14 via Frontend Transport; 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>>   } >>   -static bool dma_buf_poll_shared(struct dma_resv *resv, >> +static bool dma_buf_poll_add_cb(struct dma_resv *resv, bool write, >>                   struct dma_buf_poll_cb_t *dcb) >>   { >> -    struct dma_resv_list *fobj = dma_resv_shared_list(resv); >> +    struct dma_resv_iter cursor; >>       struct dma_fence *fence; >> -    int i, r; >> - >> -    if (!fobj) >> -        return false; >> +    int r; >>   -    for (i = 0; i < fobj->shared_count; ++i) { >> -        fence = rcu_dereference_protected(fobj->shared[i], >> -                          dma_resv_held(resv)); >> +    dma_resv_for_each_fence(&cursor, resv, write, fence) { >>           dma_fence_get(fence); >>           r = dma_fence_add_callback(fence, &dcb->cb, dma_buf_poll_cb); >>           if (!r) > > It is unchanged with this patch, but are the semantics supposed to be > like this? Signal poll event if _any_ of the shared fences has been > signaled? That had Daniel and me confused for a moment as well. We don't signal the poll when any of the shared fences has signaled, but rather install a callback on the first not-signaled fence. This callback then issues a re-test of the poll and only if we can't find any more fence the poll is considered signaled (at least that's the idea, the coding could as well be broken). Christian. > > Regards, > > Tvrtko > >> @@ -232,24 +227,6 @@ static bool dma_buf_poll_shared(struct dma_resv >> *resv, >>       return false; >>   } >>   -static bool dma_buf_poll_excl(struct dma_resv *resv, >> -                  struct dma_buf_poll_cb_t *dcb) >> -{ >> -    struct dma_fence *fence = dma_resv_excl_fence(resv); >> -    int r; >> - >> -    if (!fence) >> -        return false; >> - >> -    dma_fence_get(fence); >> -    r = dma_fence_add_callback(fence, &dcb->cb, dma_buf_poll_cb); >> -    if (!r) >> -        return true; >> -    dma_fence_put(fence); >> - >> -    return false; >> -} >> - >>   static __poll_t dma_buf_poll(struct file *file, poll_table *poll) >>   { >>       struct dma_buf *dmabuf; >> @@ -282,8 +259,7 @@ static __poll_t dma_buf_poll(struct file *file, >> poll_table *poll) >>           spin_unlock_irq(&dmabuf->poll.lock); >>             if (events & EPOLLOUT) { >> -            if (!dma_buf_poll_shared(resv, dcb) && >> -                !dma_buf_poll_excl(resv, dcb)) >> +            if (!dma_buf_poll_add_cb(resv, true, dcb)) >>                   /* No callback queued, wake up any other waiters */ >>                   dma_buf_poll_cb(NULL, &dcb->cb); >>               else >> @@ -303,7 +279,7 @@ static __poll_t dma_buf_poll(struct file *file, >> poll_table *poll) >>           spin_unlock_irq(&dmabuf->poll.lock); >>             if (events & EPOLLIN) { >> -            if (!dma_buf_poll_excl(resv, dcb)) >> +            if (!dma_buf_poll_add_cb(resv, false, dcb)) >>                   /* No callback queued, wake up any other waiters */ >>                   dma_buf_poll_cb(NULL, &dcb->cb); >>               else >>