Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 1 Feb 2021 17:37:26 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Ricardo Ribalda <ribalda@chromium.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Tomasz Figa <tfiga@chromium.org>,
        Sergey Senozhatsky <senozhatsky@google.com>,
        "list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>, Joerg
        Roedel <joro@8bytes.org>," <iommu@lists.linux-foundation.org>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH 6/6] media: uvcvideo: Use dma_alloc_noncontiguos API
Message-ID: <20210201163726.GA8279@lst.de>
References: <20210128145837.2250561-1-hch@lst.de> <20210128145837.2250561-7-hch@lst.de> <20210128150955.GA30563@lst.de> <CANiDSCtV8eiH7r6-mX3QhsYvJapqRfYufu4-iqmeiy6GiwwE_A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CANiDSCtV8eiH7r6-mX3QhsYvJapqRfYufu4-iqmeiy6GiwwE_A@mail.gmail.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Precedence: bulk

On Thu, Jan 28, 2021 at 06:00:57PM +0100, Ricardo Ribalda wrote:
> > Given that we vmap the addresses this also needs
> > flush_kernel_vmap_range / invalidate_kernel_vmap_range calls for
> > VIVT architectures.
> 
> We only read from the device to the cpu. Then can we run only
> invalidate_kernel_vmap_range() ?
> 
> something like ?
> else {
>           dma_sync_sgtable_for_cpu(dma_dev, uvc_urb->sgt, DMA_FROM_DEVICE);
>            invalidate_kernel_vmap_range(uvc_urb->buffer,
> uvc_urb->stream->urb_size );
> }

Yes.  Right now we don't have a proper state machine for the
*_kernel_vmap_range, but we should probably add one once usage of this
grows.  Until then I need to respin my API patch to document how callers
need to use *_kernel_vmap_range, as well as adding the so far missing
dma-debug support.

As we're getting toward the end of the merge window I'll try to get this
done ASAP.

How should we plan to merge this code?  Do you have a tree you'd like
to pick up the whole thing for?  Or should I create a dma-mapping
tree branch that can be pulled in?