From mboxrd@z Thu Jan 1 00:00:00 1970 From: Atish Patra Subject: Re: [RFC 1/4] pwm: sifive: Add DT documentation for SiFive PWM Controller. Date: Tue, 16 Oct 2018 15:20:34 -0700 Message-ID: <7fc1168d-a840-032a-c0a9-2a610127c484@wdc.com> References: <1539111085-25502-1-git-send-email-atish.patra@wdc.com> <1539111085-25502-2-git-send-email-atish.patra@wdc.com> <20181010134926.GD21134@ulmo> <25758ab9-eb36-741b-6264-42412b3ddd8e@wdc.com> <20181016110142.GC8852@ulmo> <6e108e3c-15c1-b13b-ac3e-60c5eb209c7b@sifive.com> <20181016220437.GB31973@mithrandir> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20181016220437.GB31973@mithrandir> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Thierry Reding , Paul Walmsley Cc: Rob Herring , mark.rutland@arm.com, linux-pwm@vger.kernel.org, devicetree@vger.kernel.org, Wesley Terpstra , linus.walleij@linaro.org, palmer@sifive.com, linux-kernel@vger.kernel.org, hch@infradead.org, linux-gpio@vger.kernel.org, linux-riscv@lists.infradead.org List-Id: linux-gpio@vger.kernel.org On 10/16/18 3:04 PM, Thierry Reding wrote: > On Tue, Oct 16, 2018 at 10:31:42AM -0700, Paul Walmsley wrote: >> >> On 10/16/18 4:01 AM, Thierry Reding wrote: >>> On Mon, Oct 15, 2018 at 03:57:35PM -0700, Atish Patra wrote: >>>> On 10/10/18 6:49 AM, Thierry Reding wrote: >>>>> On Tue, Oct 09, 2018 at 11:51:22AM -0700, Atish Patra wrote: >>>>>> +Required properties: >>>>>> +- compatible: should be one of >>>>>> + "sifive,fu540-c000-pwm0","sifive,pwm0". >>>>> What's the '0' in here? A version number? >>>>> >>>> I think yes. Since fu540 is the first Linux capable RISC-V core, SiFive Guys >>>> decided mark it as version 0. >>>> >>>> @Wesly: Please correct me if I am wrong. >>> It seems fairly superfluous to me to have a version number in additon to >>> the fu540-c000, which already seems to be the core plus some sort of >>> part number. Do you really expect there to be any changes in the SoC >>> that would require a different compatible string at this point? If the >>> SoC has taped out, how will you ever get a different version of the PWM >>> IP in it? >>> >>> I would expect any improvements or changes to the PWM IP to show up in a >>> different SoC generation, at which point it would be something like >>> "sifive,fu640-c000" maybe, or perhaps "sifive,fu540-d000", or whatever >>> the numbering is. >> >> >> The "0" suffix refers to a revision number for the underlying PWM IP block. >> >> It's certainly important to keep that version number on the "sifive,pwm0" >> compatible string that doesn't have the chip name associated with it. > > Isn't the hardware identified by "sifive,pwm0" and "sifive,fu540-c000" > effectively identical? Yes. Is there a need to have two compatible strings > that refer to the exact same hardware? > The DT in the hardware has only sifive,pwm0. I have added "sifive,fu540-c000" as that was concluded as the correct compatible string from platform level interrupt controller patch(PLIC) discussion. (http://lists.infradead.org/pipermail/linux-riscv/2018-August/001135.html) "sifive,pwm0" is required to until all the Unleashed SoC gets an updated firmware with correct compatible string "sifive,fu540-c000". I agree this is a mess. But we have to carry it until all every DT(corresponding to each driver) is finalized. I guess SiFive will release a firmware update that contains all the updated DT once that is done. We can get rid of all the redundant compatible strings at that time. Regards, Atish >> As to whether there could ever be a FU540-C000 part with different IP block >> versions on it: FU540-C000 is ultimately a marketing name.  While >> theoretically we shouldn't have another "FU540-C000" chip with different >> peripheral IP block versions on it, I don't think any engineer can guarantee >> that it won't happen. > > I would argue that if at some point there was indeed a chip with the > same name but a different IP block version in it, we can figure out what > to call it. Sure there are no guarantees, but it's still fairly unlikely > in my opinion, so I personally wouldn't worry about this up front. > > Anyway, I don't feel strongly either way, I'm just pointing out that > this is somewhat unusual. If you want to keep it, feel free to. > > Thierry >