From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Shevchenko Subject: Re: [PATCH v3 02/16] mfd: mfd-core: Don't overwrite the dma_mask of the child device Date: Tue, 28 Apr 2020 17:29:38 +0300 Message-ID: <20200428142938.GX185537@smile.fi.intel.com> References: <20200423174543.17161-1-michael@walle.cc> <20200423174543.17161-3-michael@walle.cc> <20200428124548.GS185537@smile.fi.intel.com> <3cd3705a-4f48-6a46-e869-3ee11dc17323@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <3cd3705a-4f48-6a46-e869-3ee11dc17323@arm.com> Sender: linux-gpio-owner@vger.kernel.org To: Robin Murphy Cc: Michael Walle , linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-pwm@vger.kernel.org, linux-watchdog@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Linus Walleij , Bartosz Golaszewski , Rob Herring , Jean Delvare , Guenter Roeck , Lee Jones , Thierry Reding , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Wim Van Sebroeck , Shawn Guo , Li Yang , Thomas Gleixner , Jason Cooper List-Id: linux-pwm@vger.kernel.org On Tue, Apr 28, 2020 at 02:06:20PM +0100, Robin Murphy wrote: > On 2020-04-28 1:45 pm, Andy Shevchenko wrote: > > On Thu, Apr 23, 2020 at 07:45:29PM +0200, Michael Walle wrote: > > > Commit cdfee5623290 ("driver core: initialize a default DMA mask for > > > platform device") initialize the DMA of a platform device. But if the > > > parent doesn't have a dma_mask set, for example if it's an I2C device, > > > the dma_mask of the child platform device will be set to zero again. > > > Which leads to many "DMA mask not set" warnings, if the MFD cell has the > > > of_compatible property set. > > > > I'm wondering why parent doesn't have it. > > Because the parent isn't on a DMA-capable bus, and thus really shouldn't > have a valid DMA configuration ever. Then how come a child is DMA capable? MFD takes a physical device node as a parent and creates one of several children with that device as a parent. DMA mask is a property of the device which *does DMA*. Obviously a child is not correct device for that. Where am I mistaken? > > I remember we have explicit patches in the past for buses such as PCI and AMBA > > to set default DMA mask for all physical devices on the respective bus, of > > course they can individually override it later. > > > > So, this seems to me a paper over the real issue (absence of default DMA mask > > where it's needed) and devices should explicitly define it if they disagree > > with default. > > > > If I'm wrong, you really need elaborate commit message much better. > > The problem here is that MFD children are created as platform devices > (regardless of what their parent is) and assigned an of_node, at which point > they look pretty much indistinguishable from SoC devices created by the > of_platform code, that *do* have to be assumed to be DMA-capable to prevent > ~90% of existing devicetrees from breaking. > > Of course the real fundamental issue is the platform bus itself, but it's > way too late to fix that :( I don't think it's an issue, rather in model you are describing. Or I miss something not so obvious. -- With Best Regards, Andy Shevchenko