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Date: Thu, 14 May 2015 18:34:15 +0200 From: Maxime Coquelin <mcoquelin.stm32@...il.com> To: Arnd Bergmann <arnd@...db.de> Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Daniel Thompson <daniel.thompson@...aro.org>, Mark Rutland <mark.rutland@....com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, Linus Walleij <linus.walleij@...aro.org>, Will Deacon <will.deacon@....com>, Stefan Agner <stefan@...er.ch>, Nikolay Borisov <Nikolay.Borisov@....com>, Peter Meerwald <pmeerw@...erw.net>, "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>, Lee Jones <lee.jones@...aro.org>, Mauro Carvalho Chehab <mchehab@....samsung.com>, Linux-Arch <linux-arch@...r.kernel.org>, Russell King <linux@....linux.org.uk>, Jonathan Corbet <corbet@....net>, Jiri Slaby <jslaby@...e.cz>, Daniel Lezcano <daniel.lezcano@...aro.org>, Chanwoo Choi <cw00.choi@...sung.com>, Andy Shevchenko <andy.shevchenko@...il.com>, Antti Palosaari <crope@....fi>, Geert Uytterhoeven <geert@...ux-m68k.org>, "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>, Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, Kees Cook <keescook@...omium.org>, Pawel Moll <pawel.moll@....com>, Ian Campbell <ijc+devicetree@...lion.org.uk>, Kamil Lulko <rev13@...pl>, Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo <tj@...nel.org>, Rob Herring <robh+dt@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Nicolae Rosia <nicolae.rosia@...il.com>, Michal Marek <mmarek@...e.cz>, Paul Bolle <pebolle@...cali.nl>, Peter Hurley <peter@...leysoftware.com>, "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Philipp Zabel <p.zabel@...gutronix.de>, Kumar Gala <galak@...eaurora.org>, Joe Perches <joe@...ches.com>, Andrew Morton <akpm@...ux-foundation.org>, Andreas Färber <afaerber@...e.de>, Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com> Subject: Re: [PATCH v8 14/16] ARM: dts: Introduce STM32F429 MCU 2015-05-13 21:37 GMT+02:00 Arnd Bergmann <arnd@...db.de>: > On Wednesday 13 May 2015 20:29:12 Daniel Thompson wrote: >> On 13/05/15 17:54, Maxime Coquelin wrote: >> > 2015-05-13 18:37 GMT+02:00 Arnd Bergmann <arnd@...db.de>: >> >> >> >> We should definitely try to use the same compatible string for all of >> >> them, and make a binding that is easy to use. >> >> >> >> I haven't fully understood the requirements for the various parts that >> >> are involved here. My understanding so far was that the driver could >> >> use the index from the first cell and compute >> >> >> >> void __iomem *reset_reg = rcc_base + 0x10 + 4 * index; >> >> void __iomem *clock_reg = rcc_base + 0x30 + 4 * index; >> > >> > This calculation is true, but we have to take into account there is a >> > hole in the middle, between AHB3, and APB1 register: >> >> ... and equally importantly, only allows us to use hardware mappings for >> the gated clocks. >> >> > AHB1RSTR : offset = 0x10, index = 0 >> > AHB2RSTR : offset = 0x14, index = 1 >> > AHB3RSTR : offset = 0x18, index = 2 >> > <HOLE > : offset = 0x1c, index = 3 >> > APB1RSTR : offset = 0x20, index = 4 >> > APB2RSTR : offset = 0x24, index = 5 >> > >> > So we have to carefully document this hole in the bindings, maybe by >> > listing indexes in the documentation? >> >> The register set has PLL, mux and dividers in the registers at 0x00, >> 0x04 and 0x08. >> >> Many of these clocks can be kept out of DT entirely because they are >> only there to feed other parts of the clock tree. However some of the >> dividers flow directly into cells that appear in device tree (such as >> the systick) and so we need to be able to reference them. >> >> In other words the proposed mapping cannot allow us to express the >> dividers properly (because the index would have to be negative): >> void __iomem *clock_reg = rcc_base + 0x30 + 4 * index; >> >> Thus I'd favour using different indexes for reset and clock bindings, >> both using the naive mapping function: >> void __iomem *reg = rcc_base + 4 * index >> >> I think that its so much easier to check against the datasheet like >> that. Admittedly is we follow the block-of-4-bytes idiom we have to >> divide a hex number by four but thats not so hard and we end up with: >> >> resets = <&rcc 8 0>; >> clocks = <&rcc 16 0>; >> >> At the end of the day if we say we want to follow the datasheet, lets be >> do it in the most direct way properly. Daniel, I'm fine with your proposal. Doing that, we can have a single compatible string for stm32 family, even if the reset start offset change between two chips. >> >> >> PS >> I've written a custom lookup function to to get from the DT index to an >> offset into the struct clk *array I'm using. That means I don't care >> much about any big holes in the register space. > > How about using the first cell to indicate the type (pll, mux, div, gate) > and the second cell for the number (between 0 and 256)? That way, the > gates numbers would match the reset numbers, and your internal mapping > function would look a bit nicer. That's another option. In this case, for reset, we will only need one cell, right? Regards, Maxime > > Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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