From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0EEC6C04EBD for ; Tue, 16 Oct 2018 11:01:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B5B512086E for ; Tue, 16 Oct 2018 11:01:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="HijZaiu5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B5B512086E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727165AbeJPSvk (ORCPT ); Tue, 16 Oct 2018 14:51:40 -0400 Received: from mail-wr1-f68.google.com ([209.85.221.68]:43954 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726581AbeJPSvj (ORCPT ); Tue, 16 Oct 2018 14:51:39 -0400 Received: by mail-wr1-f68.google.com with SMTP id n1-v6so24963599wrt.10; Tue, 16 Oct 2018 04:01:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=fnGCS83Z0SZAGsiz42xG0H+2VU7WB1tZuj9DdgTIoQQ=; b=HijZaiu5sP3vZtlCbpQZqyDsGFpqIRHQgyMltErHDYKNDutFb6azEo8VWcnZxd2HPx x3idSsHg0FEecmvOeEtF+ayf1448eR/5B4WThHpMoY2b51hdjAqJhfR7CnPBk4MYl8KX lQmCEkKamsvEETtB/xtK07w1qfQpxsS3idFMb32Yph9yC1kPRbPu7PXEbraYL232zBkb 2Vj61TBwHnC5+A1SqriQa/PP4xuZ/lKezYqu4HdgqDAcHpoBhHQGawH2pgc1tE5veLoY DAF3XE+qtpJsX0RMLiCJrWEwiZM+IzIG6eqv+NEoHydy3uXzjvkQSk/f5y3CMOATWM3U yfgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=fnGCS83Z0SZAGsiz42xG0H+2VU7WB1tZuj9DdgTIoQQ=; b=NPx0cBO4g5NagfbQUX/WI1xQ88zIIuA2ET4UuhOvHxgCsODzlSNiJtv4JEblCFvfZM gRGEC7jYPQLOm4FuyE6oVJFmMkOT9QvA/tuaYMVNFUCV3hvudp8UM+xphj/RUnsgKxBX WaAx6gj8y8aGJ5bpc5TeCuZ89MWZ1gXEccLxiTo5ypzrJaNtuHbfzv/5JOPJIo59S9dg N8YFfq7ZOz/WECwJlne2T3eSXOcj5cmRRslyO47ox7vjs+ZmJRcQ7uqlOAHJYtukbdNJ mTyvbWQhzaKNGYwGttro4+KeBv9A9vt+jhQ5GC2v9ukSrMIkojL7UGwn6sB+IcFd59Hz oEEg== X-Gm-Message-State: ABuFfogLde/Mx/MfeBICpULfbbo7FIf7iNw3oBhr7DDEzhmfJfF9CBCw QyJZfGQz3WswXYmS7eegmK8= X-Google-Smtp-Source: ACcGV60XPHlPvtT49HYyLOubtJz18+BHFeC1YnHOQgMbaW99bDWRvBFlBT3htyhCBzTfO1CtCq3UIg== X-Received: by 2002:a5d:4208:: with SMTP id n8-v6mr17033485wrq.260.1539687704113; Tue, 16 Oct 2018 04:01:44 -0700 (PDT) Received: from localhost (pD9E5106D.dip0.t-ipconnect.de. [217.229.16.109]) by smtp.gmail.com with ESMTPSA id 126-v6sm11977018wme.48.2018.10.16.04.01.42 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 16 Oct 2018 04:01:43 -0700 (PDT) Date: Tue, 16 Oct 2018 13:01:42 +0200 From: Thierry Reding To: Atish Patra , Rob Herring Cc: Wesley Terpstra , palmer@sifive.com, linux-riscv@lists.infradead.org, linux-pwm@vger.kernel.org, linux-gpio@vger.kernel.org, linus.walleij@linaro.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, hch@infradead.org Subject: Re: [RFC 1/4] pwm: sifive: Add DT documentation for SiFive PWM Controller. Message-ID: <20181016110142.GC8852@ulmo> 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> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Pk6IbRAofICFmK5e" Content-Disposition: inline In-Reply-To: <25758ab9-eb36-741b-6264-42412b3ddd8e@wdc.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Pk6IbRAofICFmK5e Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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: > > > From: "Wesley W. Terpstra" > > >=20 > > > DT documentation for PWM controller added with updated compatible > > > string. > > >=20 > > > Signed-off-by: Wesley W. Terpstra > > > [Atish: Compatible string update] > > > Signed-off-by: Atish Patra > > > --- > > > .../devicetree/bindings/pwm/pwm-sifive.txt | 32 +++++++++++= +++++++++++ > > > 1 file changed, 32 insertions(+) > > > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive= =2Etxt > > >=20 > > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/D= ocumentation/devicetree/bindings/pwm/pwm-sifive.txt > > > new file mode 100644 > > > index 00000000..532b10fc > > > --- /dev/null > > > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > @@ -0,0 +1,32 @@ > > > +SiFive PWM controller > > > + > > > +Unlike most other PWM controllers, the SiFive PWM controller current= ly only > > > +supports one period for all channels in the PWM. This is set globall= y in DTS. > > > +The period also has significant restrictions on the values it can ac= hieve, > > > +which the driver rounds to the nearest achievable frequency. > >=20 > > What restrictions are these? If "nearest achievable" is too far off the > > target period it might be preferable to error out. > >=20 >=20 > @Wes: Any comments? >=20 > > > +Required properties: > > > +- compatible: should be one of > > > + "sifive,fu540-c000-pwm0","sifive,pwm0". > >=20 > > What's the '0' in here? A version number? > >=20 >=20 > I think yes. Since fu540 is the first Linux capable RISC-V core, SiFive G= uys > decided mark it as version 0. >=20 > @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. > > > + PWM controller is HiFive Unleashed specific chip which warrants a > > > + specific compatible string. The second string is kept for backward > > > + compatibility until a firmware update with latest compatible string. > > > +- reg: physical base address and length of the controller's registers > > > +- clocks: The frequency the controller runs at > > > +- #pwm-cells: Should be 2. > > > + The first cell is the PWM channel number > > > + The second cell is the PWM polarity > > > +- sifive,approx-period: the driver will get as close to this period = as it can > >=20 > > Given the above comment, maybe "sifive,period"? > >=20 >=20 > ok. > In Unleashed board, the DT is loaded by FSBL (first stage boot loader). > Thus, changing device tree entries requires a FSBL update. If we update t= his > string, we need to update the driver to parse both properties so that > existing devices with older firmware continue to work. >=20 > This is probably ok as we anyways do that for compatible strings. Just > wanted to update that here for the record. I'm going to defer to Rob on this. He's said in the past that he doesn't care about existing bindings that haven't been vetted through upstream, even if that means that bootloaders may have to be updated. I know he's been fairly strict on this in the past, but let's see if there is room for exceptions. 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