From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marek Vasut Subject: Re: Forcing PIO mode instead of DMA via DT property Date: Mon, 30 Jul 2012 16:00:44 +0200 Message-ID: <201207301600.45000.marex@denx.de> References: <201207222328.27008.marex@denx.de> <201207240617.31565.marex@denx.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: "devicetree-discuss" To: Aggrwal Poonam-B10812 Cc: "pavel-ynQEQJNshbs@public.gmane.org" , "devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org" , Wolfgang Denk List-Id: devicetree@vger.kernel.org Dear Aggrwal Poonam-B10812, [...] > > > > We just had such a situation, where PIO had to be used on a specific > > > > bus, because due to a hardware problem (board design error) DMA > > > > would crash the system. Yet the same driver/kernel would work fine > > > > with DMA on other buses / boards. OK, this was on x86, so DT would > > > > not have helped, but I think a bus-specific property of being able > > > > to do DMA (or not) might indeed make sense for the DT. > > > > > > In that case probably we can use QUIRKS like broken-dma. I see this in > > > the sdhc driver in Linux. On P2020 chip(rev 1.0) of FSL DMA was broken > > > so we used this to force PIO. > > > > Do you please happen to have any sample of such DT binding for reference? > > Sorry cannot find the DT bindings in upstream, probably this issue was not > there in P2020 Rev2.0 hence so. I can cite a node from FSL old SDK > sdhci@2e000 { > compatible = "fsl,p2020-esdhc", "fsl,esdhc"; > reg = <0x2e000 0x1000>; > interrupts = <72 0x2>; > interrupt-parent = <&mpic>; > fsl,sdhci-adjust-timeout; > /* Filled in by U-Boot */ > clock-frequency = <0>; > }; > > > > You can look at drivers/mmc/host/sdhci-of-esdhc.c which handles various > quirks. Ok, so you suggest we add such a property or what is the conclusion please? Best regards, Marek Vasut