From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Jones Subject: Re: [PATCH 09/33] ARM: ux500: Supply the I2C clocks lookup to the DBX500 DT Date: Tue, 27 Aug 2013 15:08:05 +0100 Message-ID: <20130827140805.GB10210@lee--X1> References: <20130820093034.GL31036@pengutronix.de> <20130822133730.GB23152@e106331-lin.cambridge.arm.com> <20130822141900.GB17154@lee--X1> <20130822151723.GE23152@e106331-lin.cambridge.arm.com> <20130822154116.GC17154@lee--X1> <20130822211912.GE31036@pengutronix.de> <20130823075607.GD17154@lee--X1> <20130823165539.GD7015@e106331-lin.cambridge.arm.com> <20130827080635.GC6152@lee--X1> <20130827134621.GJ19893@e106331-lin.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20130827134621.GJ19893@e106331-lin.cambridge.arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Mark Rutland Cc: Sascha Hauer , Linus Walleij , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Arnd Bergmann , "devicetree@vger.kernel.org" List-Id: devicetree@vger.kernel.org On Tue, 27 Aug 2013, Mark Rutland wrote: > On Tue, Aug 27, 2013 at 09:06:35AM +0100, Lee Jones wrote: > > On Fri, 23 Aug 2013, Mark Rutland wrote: > >=20 > > > On Fri, Aug 23, 2013 at 08:56:07AM +0100, Lee Jones wrote: > > > > I had a short chat with Rob last night about this. I'm going to= loop > > > > him in to the conversation, as he wrote the binding. > > > >=20 > > > > > > When most of the other clocks that we deal with are being r= equested, > > > > > > they rely on being index zero: > > > > > >=20 > > > > > > drivers/i2c/busses/i2c-nomadik.c: dev->clk =3D clk_get(&a= dev->dev, NULL); > > > > >=20 > > > > > Look at drivers/clk/clkdev.c, there's some fuzzy matching > > > > > involved when you pass NULL as connection id. > > > >=20 > > > > Yes, I've been looking at that. This is why it works currently.= I > > > > think I need to change all of the drivers to specify which cloc= k they > > > > want. At the moment that 'fuzzy matching' is what's saving us. = If > > > > anyone were to change our DTS file to match what the binding sa= ys, > > > > then it would cease to work. I'm guessing this is the same for = all > > > > other DTS files too: > > >=20 > > > I think if anything, the binding document(s) should be updated to > > > describe that apb_pclk is referred to by name, and the names of t= he > > > other clocks should be described in the specific device bindings.= We can > > > then modify the drivers which grab clock 0 to explicitly grab the= first > > > clock by name, and backwards compatibility should not be broken. > > >=20 > > > I don't believe any other OS has implemented the common clock bin= dings, > > > and we've never supported the binding as described. Let's correct= the > > > de-facto standard into a standard by decree. > >=20 > > I think we need to respect, or at least take into consideration the > > reason for the original 'de-facto' standard. Other OSes shouldn't b= e > > forced to provide a named clock request in order to obtain > > 'apb_pclk'. If the binding says it should be first, then perhaps we > > should do just that. It's simply a matter of naming all subsequent > > clocks related to AMBA devices. >=20 > Ideally, yes. However, we have to be careful to not break compatibili= ty. >=20 > I took a look at existing primecell drivers and what they do. The > situation isn't so bad (with the exception of the > half-dt/half-platform-code mess): >=20 > * Some don't deal with clocks at all (no clk* in the driver). pl320 i= s > in the ecx-common dtsi with only apb_pclk but has no binding > defined. Some have no clocks defined in the dt and are presumably f= ew > clocks by platform data or are non-functional. >=20 > I'm not sure how these DTs are going to be supported if and when we > remove the platform data they depend upon. If we're really going to= do > that, then they are clearly not supported as-is long term. >=20 > * The pl022 driver grabs the first clock to figure out the rate of th= e > spi bus (assuming it is SSPCLK). The SSPCLK input is not defined in > the binding. The ste-u300 dts has two clock-names, "apb_pclk" and > "spi_clk" (in that order), but they refer to the same clock. >=20 > Given the existing driver simply grabs the first clock and they're > both the same, we could re-order the names and make the driver grab > the second clock. That wouldn't break backwards compatibility with = the > sole dts file we have using the binding, though this assumes no-one > else has a dt lying around with different clocks. >=20 > * pl010 grabs the first clock given to it to figure out the uart rate > (assuming it is UARTCLK), but it's only in integratorap.dts, withou= t > clocks, and is presumably fed by platform data. There is no binding > document. >=20 > pl011 grabs the first clock given to figure out the UART rate > (assuming it is UARTCLK). The binding explicitly states it's only > given apb_pclk, despite UARTCLK and PCLK being separate inputs to t= he > IP block. >=20 > These two bindings don't describe the hardware, and should be fixed= =2E > The only way I can think to make this work without breaknig backwar= ds > compatibility would be to try to grab the second clock and then fal= l > back to the first if there isn't one. The other option is to break > backwards compatibility, but I'm not sure that's much of an option. >=20 > * pl111 has no driver or binding in mainline, but appears in dts file= s. > Those dts files clcdclk and apb_pclk, in that order. We could fix > those before a driver starts using them. >=20 > If you think those suggestions are OK, I can put together a series to > fix this. I think we need to hear from Rob before we proceed tbh, as he is the original author and should have a chance to voice his opinion. --=20 Lee Jones Linaro ST-Ericsson Landing Team Lead Linaro.org =E2=94=82 Open source software for ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog