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Date:   Mon, 23 Sep 2019 17:20:54 +0200
From:   Thierry Reding <thierry.reding@gmail.com>
To:     Sam Shih <sam.shih@mediatek.com>
Cc:     Mark Rutland <mark.rutland@arm.com>, linux-pwm@vger.kernel.org,
        Ryder Lee <ryder.lee@mediatek.com>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
        linux-mediatek@lists.infradead.org,
        John Crispin <john@phrozen.org>,
        Matthias Brugger <matthias.bgg@gmail.com>
Subject: Re: [PATCH v9 07/11] dt-bindings: pwm: pwm-mediatek: add a property
 "num-pwms"
Message-ID: <20190923152054.GA17178@ulmo>
References: <1568933351-8584-1-git-send-email-sam.shih@mediatek.com>
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On Mon, Sep 23, 2019 at 11:11:55PM +0800, Sam Shih wrote:
> On Mon, 2019-09-23 at 15:36 +0200, Thierry Reding wrote:
> > On Mon, Sep 23, 2019 at 11:20:57AM +0800, Sam Shih wrote:
> > > On Sat, 2019-09-21 at 02:21 +0200, Thierry Reding wrote:
> > > > On Fri, Sep 20, 2019 at 06:49:07AM +0800, Sam Shih wrote:
> > > > > From: Ryder Lee <ryder.lee@mediatek.com>
> > > > >=20
> > > > > This adds a property "num-pwms" in example so that we could
> > > > > specify the number of PWM channels via device tree.
> > > > >=20
> > > > > Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
> > > > > Signed-off-by: Sam Shih <sam.shih@mediatek.com>
> > > > > Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
> > > > > Acked-by: Uwe Kleine-K=C3=B6nig <u.kleine-koenig@pengutronix.de>
> > > > > ---
> > > > > Changes since v6:
> > > > > Follow reviewers's comments:
> > > > > - The subject should indicate this is for Mediatek
> > > > >=20
> > > > > Changes since v5:
> > > > > - Add an Acked-by tag
> > > > > - This file is original v4 patch 5/10
> > > > > (https://patchwork.kernel.org/patch/11102577/)
> > > > >=20
> > > > > ---
> > > > >  Documentation/devicetree/bindings/pwm/pwm-mediatek.txt | 7 ++++-=
--
> > > > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > >=20
> > > > You failed to address Rob's questions repeatedly and I agree with h=
im
> > > > that you can just as easily derive the number of PWMs from the spec=
ific
> > > > compatible string. I won't be applying this and none of the patches=
 that
> > > > depend on it.
> > > >=20
> > >=20
> > > Hi,=20
> > >=20
> > > Thanks for getting back to me.
> > >=20
> > > New pwm driver (patch 04/11 : "pwm: mediatek: allocate the clks array
> > > dynamically") can support different variants with different number of
> > > PWMs by the new property <num-pwms>
> > >=20
> > > For example:
> > > 1. Use "num-pwms" =3D <2> and assign clocks pwm1, pwm2 for mt7622
> > > 2. Use "num-pwms" =3D <6> and assign clocks pwm1, pwm2, pwm3, pwm4, p=
wm5,
> > > pwm6 for mt7622.
> > >=20
> > > If we just as easily derive the number of PWMs from the specific
> > > compatible string in this document:
> > >=20
> > >    - "pwm1-6": the six per PWM clocks for mt7622
> > >   =20
> > > This looks like all "pwm1", "pwm2", "pwm3", "pwm4", "pwm5", "pwm6" is
> > > required property in DT, It doesn't make sense.
> >=20
> > I don't understand. Why doesn't that make sense? If your hardware block
> > has 6 PWMs and each can be driven by its own clock, then you need to
> > provide references for each of those clocks, otherwise you won't be able
> > to use them.
>=20
> Thank you for your instruction,
> I will add all clock-names and clocks according to
> hardware blocks instead of value of <num-pwms> in DT.
>=20
> > >   =20
> > > So we removed those descriptions and added =20
> > >=20
> > >    - "pwm1-N": the PWM clocks for each channel=20
> > >   =20
> > >   =20
> > > But the max number of clocks from the compatible string are still
> > > important information that should be provide in this document.
> > >=20
> > >=20
> > > What do you think of this?
> > >=20
> > >    - "pwm1-N": per PWM clocks for mt2712, the max number of PWM chann=
els
> > > is 8
> > >=20
> > >    - "pwm1-N": per PWM clocks for mt7622, the max number of PWM chann=
els
> > > is 6
> > >=20
> > >    - "pwm1-N": per PWM clocks for mt7623, the max number of PWM chann=
els
> > > is 5
> >=20
> > That's what's in the bindings already, isn't it?
> >=20
> > 	 - clocks: phandle and clock specifier of the PWM reference clock.
> > 	 - clock-names: must contain the following, except for MT7628 which
> > 			has no clocks
> > 	   - "top": the top clock generator
> > 	   - "main": clock used by the PWM core
> > 	   - "pwm1-8": the eight per PWM clocks for mt2712
> > 	   - "pwm1-6": the six per PWM clocks for mt7622
> > 	   - "pwm1-5": the five per PWM clocks for mt7623
>=20
> Yes, You are right,=20
> I will keep original description and remove "pwm1-N" from this patch.
> 	   - "top": the top clock generator
> 	   - "main": clock used by the PWM core
> 	   - "pwm1-8": the eight per PWM clocks for mt2712
> 	   - "pwm1-6": the six per PWM clocks for mt7622
> 	   - "pwm1-5": the five per PWM clocks for mt7623      =20
>=20
> Actually, MT7629 also use "mediatek,mt7622-pwm" as compatible string,
> but it's hardware only support one pwm, so I was wrongly stick by
> expecting "pwm1-N" in clock-names based on "num-pwms" in DT.
> (that we can assign num-pwms to 1 and only provide pwm1 as clock-names)
>=20
> Maybe added mt7629 description to this document can solve this simply.
> 	   - "pwm1": the PWM1 clock for mt7629   =20

Yeah, if mt7629 support only one PWM channel, you should list it's
compatible string separately and also update the driver to reflect the
number of channels associated with the hardware.

Thierry

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