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[209.85.166.43]) by smtp.gmail.com with ESMTPSA id h70sm5586066iof.31.2020.11.30.02.49.20 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 Nov 2020 02:49:20 -0800 (PST) Received: by mail-io1-f43.google.com with SMTP id d8so10053524ioc.13 for ; Mon, 30 Nov 2020 02:49:20 -0800 (PST) X-Received: by 2002:a02:c042:: with SMTP id u2mr12243455jam.32.1606733360204; Mon, 30 Nov 2020 02:49:20 -0800 (PST) MIME-Version: 1.0 References: <20201125221917.150463-1-ribalda@chromium.org> <20201130083410.GD32234@lst.de> In-Reply-To: <20201130083410.GD32234@lst.de> From: Ricardo Ribalda Date: Mon, 30 Nov 2020 11:49:09 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API To: Christoph Hellwig Cc: Marek Szyprowski , Robin Murphy , Mauro Carvalho Chehab , IOMMU DRIVERS , Joerg Roedel , Linux Doc Mailing List , Linux Kernel Mailing List , Linux Media Mailing List , Tomasz Figa , Sergey Senozhatsky Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Christoph On Mon, Nov 30, 2020 at 9:34 AM Christoph Hellwig wrote: > > > +#ifndef CONFIG_DMA_NONCOHERENT > > I think you need to drop this ifdef. This code should work just fine > on noncoherent mips and sh platforms. > > > + uvc_urb->pages = dma_alloc_noncontiguous(dma_dev, stream->urb_size, > > + &uvc_urb->dma, > > + gfp_flags | __GFP_NOWARN, 0); > > + if (!uvc_urb->pages) > > + return false; > > + > > + uvc_urb->buffer = vmap(uvc_urb->pages, > > + PAGE_ALIGN(stream->urb_size) >> PAGE_SHIFT, > > + VM_DMA_COHERENT, PAGE_KERNEL); > > + if (!uvc_urb->buffer) { > > + dma_free_noncontiguous(dma_dev, stream->urb_size, > > + uvc_urb->pages, uvc_urb->dma); > > + return false; > > + } > > + > > + if (sg_alloc_table_from_pages(&uvc_urb->sgt, uvc_urb->pages, > > + PAGE_ALIGN(stream->urb_size) >> PAGE_SHIFT, 0, > > + stream->urb_size, GFP_KERNEL)) { > > + vunmap(uvc_urb->buffer); > > + dma_free_noncontiguous(dma_dev, stream->urb_size, > > + uvc_urb->pages, uvc_urb->dma); > > + return false; > > + } > > + > > + return true; > > +} > > I wonder if we should lift this into a helper. On the one hand I had > proliferating struct scatterlist usage, on the other hand it is all over > the media and drm code anyway, and duplicating this doesn't help anyone. > > Possibly including the fallback to the coherent allocating. Probably Sergey has best opinion of this than mine. I only had to look into one driver, he has been working with the vb2, which uses the API much more. -- Ricardo Ribalda