From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Iwai Date: Sat, 03 Aug 2019 11:22:09 +0000 Subject: Re: [PATCH 5/5] dma-mapping: remove ARCH_NO_COHERENT_DMA_MMAP Message-Id: List-Id: References: <20190725063401.29904-1-hch@lst.de> <20190725063401.29904-6-hch@lst.de> <20190802070354.GA8280@lst.de> <20190803103024.GA32624@lst.de> In-Reply-To: <20190803103024.GA32624@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Christoph Hellwig Cc: linux-xtensa@linux-xtensa.org, Michal Simek , linux-parisc@vger.kernel.org, linux-sh@vger.kernel.org, linux-m68k@lists.linux-m68k.org, Robin Murphy , x86@kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Marek Szyprowski On Sat, 03 Aug 2019 12:30:24 +0200, Christoph Hellwig wrote: > > On Fri, Aug 02, 2019 at 10:24:02AM +0200, Takashi Iwai wrote: > > I wasn't careful enough to look at that change, sorry. > > > > The code there tries to check whether dma_mmap_coherent() would always > > fail on some platforms. Then the driver clears the mmap capability > > flag at the device open time and notifies user-space to fall back to > > the dumb read/write mode. > > > > So I'm afraid that simply dropping the check would cause the behavior > > regression, e.g. on PARISC. > > > > Is there any simple way to test whether dma_mmap_coherent() would work > > or not in general on the target platform? It's not necessarily in an > > ifdef at all. > > This isn't really a platform, but a per-device question. I can add a > "bool dma_can_mmap(struct device *dev)" helper to check that. Yes, this would fit perfect. > But how > do I get at a suitable struct device in hw_support_mmap()? substream->dma_buffer.dev.dev can be that, which is used in the mmap helper side, snd_pcm_lib_default_mmap(). Thanks! Takashi