From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Date: Tue, 01 Sep 2020 15:40:49 +0000 Subject: Re: [PATCH v2] mmc: mmc_spi: Allow the driver to be built when CONFIG_HAS_DMA is unset Message-Id: <20200901154049.GA376@lst.de> List-Id: References: <20200901150438.228887-1-ulf.hansson@linaro.org> <20200901150654.GB30034@lst.de> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Ulf Hansson Cc: Christoph Hellwig , "linux-mmc@vger.kernel.org" , Rich Felker , Mark Brown , Linux-sh list , Linux Kernel Mailing List On Tue, Sep 01, 2020 at 05:36:17PM +0200, Ulf Hansson wrote: > > I still don't think this makes sense, as the dma_mask should always > > be non-NULL here. > > If that is the case, I wonder how the driver could even have worked without DMA. > > Because in the existing code, host->dma_dev gets assigned to > spi->master->dev.parent->dma_mask - which seems to turn on the DMA > usage in the driver. > > What am I missing? Do you know of other non-DMA users? For SH nommu it probably worked because SH nommu used to provide a DMA implementation that worked fine for streaming maps, but was completely broken for coherent allocation. And this driver appears to only use the former.