From: "Jernej Škrabec" <jernej.skrabec@siol.net>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: linux-sunxi@googlegroups.com, Chen-Yu Tsai <wens@csie.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-pwm@vger.kernel.org,
devicetree <devicetree@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Maxime Ripard <mripard@kernel.org>,
Rob Herring <robh+dt@kernel.org>,
Thierry Reding <thierry.reding@gmail.com>,
kernel@pengutronix.de,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [linux-sunxi] Re: [PATCH 4/6] pwm: sun4i: Add support for H6 PWM
Date: Mon, 29 Jul 2019 20:46:25 +0200 [thread overview]
Message-ID: <173825848.1FZsmuHfpq@jernej-laptop> (raw)
In-Reply-To: <20190729184041.vlvfz3vz3ykhufdk@pengutronix.de>
Dne ponedeljek, 29. julij 2019 ob 20:40:41 CEST je Uwe Kleine-König
napisal(a):
> On Mon, Jul 29, 2019 at 06:40:15PM +0200, Jernej Škrabec wrote:
> > Dne ponedeljek, 29. julij 2019 ob 18:24:28 CEST je Uwe Kleine-König
> >
> > napisal(a):
> > > Hello,
> > >
> > > On Tue, Jul 30, 2019 at 12:09:40AM +0800, Chen-Yu Tsai wrote:
> > > > On Tue, Jul 30, 2019 at 12:07 AM Uwe Kleine-König
> > > >
> > > > <u.kleine-koenig@pengutronix.de> wrote:
> > > > > On Mon, Jul 29, 2019 at 05:55:52PM +0200, Jernej Škrabec wrote:
> > > > > > Dne ponedeljek, 29. julij 2019 ob 08:40:30 CEST je Uwe
> > > > > > Kleine-König
> > > > > >
> > > > > > napisal(a):
> > > > > > > On Fri, Jul 26, 2019 at 08:40:43PM +0200, Jernej Skrabec wrote:
> > > > > > > > --- a/drivers/pwm/pwm-sun4i.c
> > > > > > > > +++ b/drivers/pwm/pwm-sun4i.c
> > > > > > > > @@ -331,6 +331,13 @@ static const struct sun4i_pwm_data
> > > > > > > > sun4i_pwm_single_bypass = {>
> > > > > > > >
> > > > > > > > .npwm = 1,
> > > > > > > >
> > > > > > > > };
> > > > > > > >
> > > > > > > > +static const struct sun4i_pwm_data
> > > > > > > > sun50i_pwm_dual_bypass_clk_rst
> > > > > > > > = {
> > > > > > > > + .has_bus_clock = true,
> > > > > > > > + .has_prescaler_bypass = true,
> > > > > > > > + .has_reset = true,
> > > > > > > > + .npwm = 2,
> > > > > > > > +};
> > > > > > > > +
> > > > > > > >
> > > > > > > > static const struct of_device_id sun4i_pwm_dt_ids[] = {
> > > > > > > >
> > > > > > > > {
> > > > > > > >
> > > > > > > > .compatible = "allwinner,sun4i-a10-pwm",
> > > > > > > >
> > > > > > > > @@ -347,6 +354,9 @@ static const struct of_device_id
> > > > > > > > sun4i_pwm_dt_ids[] =
> > > > > > > > {
> > > > > > > >
> > > > > > > > }, {
> > > > > > > >
> > > > > > > > .compatible = "allwinner,sun8i-h3-pwm",
> > > > > > > > .data = &sun4i_pwm_single_bypass,
> > > > > > > >
> > > > > > > > + }, {
> > > > > > > > + .compatible = "allwinner,sun50i-h6-pwm",
> > > > > > > > + .data = &sun50i_pwm_dual_bypass_clk_rst,
> > > > > > >
> > > > > > > If you follow my suggestion for the two previous patches, you
> > > > > > > can
> > > > > > > just
> > > > > > >
> > > > > > > use:
> > > > > > > compatible = "allwinner,sun50i-h6-pwm",
> > > > > > > "allwinner,sun5i-a10s-pwm";
> > > > > > >
> > > > > > > and drop this patch.
> > > > > >
> > > > > > Maxime found out that it's not compatible with A10s due to
> > > > > > difference
> > > > > > in bypass bit, but yes, I know what you mean.
> > > > > >
> > > > > > Since H6 requires reset line and bus clock to be specified, it's
> > > > > > not
> > > > > > compatible from DT binding side. New yaml based binding must
> > > > > > somehow
> > > > > > know that in order to be able to validate DT node, so it needs
> > > > > > standalone compatible. However, depending on conclusions of other
> > > > > > discussions, this new compatible can be associated with already
> > > > > > available quirks structure or have it's own.> >
> > > > >
> > > > > I cannot follow. You should be able to specify in the binding that
> > > > > the
> > > > > reset line and bus clock is optional. Then allwinner,sun50i-h6-pwm
> > > > > without a reset line and bus clock also verifies, but this doesn't
> > > > > really hurt (and who knows, maybe the next allwinner chip needs
> > > > > exactly
> > > > > this).
> > > >
> > > > It is not optional. It will not work if either the clocks or reset
> > > > controls
> > > > are missing. How would these be optional anyway? Either it's connected
> > > > and
> > > > thus required, or it's not and therefore should be omitted from the
> > > > description.
> > >
> > > [Just arguing about the clock here, the argumentation is analogous for
> > > the reset control.]
> > >
> > > From the driver's perspective it's optional: There are devices with and
> > > without a bus clock. This doesn't mean that you can just ignore this
> > > clock if it's specified. It's optional in the sense "If dt doesn't
> > > specify it, then assume this is a device that doesn't have it and so you
> > > don't need to handle it." but not in the sense "it doesn't matter if
> > > you handle it or not.".
> > >
> > > Other than that I'm on your side. So for example I think it's not
> > > optimal that gpiod_get_optional returns NULL if GPIOLIB=n or that
> > > devm_reset_control_get_optional returns NULL if RESET_CONTROLLER=n
> > > because this hides exactly the kind of problem you point out here.
> >
> > I think there's misunderstanding. I only argued that we can't use
> >
> > compatible = "allwinner,sun50i-h6-pwm",
> >
> > "allwinner,sun5i-a10s-pwm";
> >
> > as you suggested and only
> >
> > compatible = "allwinner,sun50i-h6-pwm";
> >
> > will work. Not because of driver itself (it can still use _optional()
> > variants), but because of DT binding, which should be able to validate H6
> > PWM node - reset and bus clock references are required in this case.
>
> I think I understood. In my eyes there is no need to let validation of
> the DT bindings catch a missing "optional" property that is needed on
> H6.
>
> You have to draw the line somewhere which information the driver has
> hard-coded and what is only provided by the device tree and just assumed
> to be correct by the driver. You argue the driver should know that
No, in this thread I argue that DT validation tool, executed by
make ARCH=arm64 dtbs_check
should catch that. This is not a driver, but DT binding described in YAML.
Best regards,
Jernej
> if it
> cares for a "allwinner,sun50i-h6-pwm" device it should know (and check)
> that there is a clock named "bus" and a resets property that links to a
> reset controller. How is that different from checking that the base
> address is 0x0300a000 or that the "pwm" clock is the osc24M clock
> running at 24 MHz? This isn't checked in the driver or the dt schema.
> Still if the device tree got one of them wrong this yields an
> non-working pwm device that isn't catched in the driver.
>
> Best regards
> Uwe
next prev parent reply other threads:[~2019-07-29 18:46 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 18:40 [PATCH 0/6] pwm: sun4i: Add support for Allwinner H6 Jernej Skrabec
2019-07-26 18:40 ` [PATCH 1/6] dt-bindings: pwm: allwinner: Add H6 PWM description Jernej Skrabec
2019-07-27 10:42 ` Maxime Ripard
2019-07-26 18:40 ` [PATCH 2/6] pwm: sun4i: Add a quirk for reset line Jernej Skrabec
2019-07-27 10:42 ` Maxime Ripard
2019-07-29 6:36 ` Uwe Kleine-König
2019-07-29 6:43 ` Chen-Yu Tsai
2019-07-29 7:12 ` Uwe Kleine-König
2019-07-29 10:18 ` Philipp Zabel
2019-07-29 16:37 ` Maxime Ripard
2019-07-29 18:20 ` Uwe Kleine-König
2019-07-26 18:40 ` [PATCH 3/6] pwm: sun4i: Add a quirk for bus clock Jernej Skrabec
2019-07-27 10:46 ` Maxime Ripard
2019-07-27 14:15 ` Jernej Škrabec
2019-07-27 14:27 ` Chen-Yu Tsai
2019-07-29 6:38 ` Uwe Kleine-König
2019-07-29 15:48 ` Jernej Škrabec
2019-07-29 16:14 ` Uwe Kleine-König
2019-07-29 16:45 ` Maxime Ripard
2019-07-29 19:04 ` Uwe Kleine-König
2019-07-26 18:40 ` [PATCH 4/6] pwm: sun4i: Add support for H6 PWM Jernej Skrabec
2019-07-29 6:40 ` Uwe Kleine-König
2019-07-29 15:55 ` Jernej Škrabec
2019-07-29 16:07 ` Uwe Kleine-König
2019-07-29 16:09 ` [linux-sunxi] " Chen-Yu Tsai
2019-07-29 16:24 ` Uwe Kleine-König
2019-07-29 16:40 ` Jernej Škrabec
2019-07-29 18:40 ` Uwe Kleine-König
2019-07-29 18:46 ` Jernej Škrabec [this message]
2019-07-29 18:51 ` Uwe Kleine-König
2019-07-29 22:04 ` Jernej Škrabec
2019-07-30 8:09 ` Uwe Kleine-König
2019-07-30 8:32 ` Chen-Yu Tsai
2019-07-30 17:06 ` Maxime Ripard
2019-07-31 6:52 ` Uwe Kleine-König
2019-08-12 9:56 ` Maxime Ripard
2019-08-12 10:47 ` Uwe Kleine-König
2019-08-12 10:51 ` Jernej Škrabec
2019-07-26 18:40 ` [PATCH 5/6] pwm: sun4i: Add support to output source clock directly Jernej Skrabec
2019-07-27 10:50 ` Maxime Ripard
2019-07-27 14:28 ` Jernej Škrabec
2019-07-27 14:54 ` [linux-sunxi] " Chen-Yu Tsai
2019-07-29 7:06 ` Uwe Kleine-König
2019-07-29 16:16 ` Jernej Škrabec
2019-07-29 16:29 ` Uwe Kleine-König
2019-07-26 18:40 ` [PATCH 6/6] arm64: dts: allwinner: h6: Add PWM node Jernej Skrabec
2019-07-27 10:51 ` Maxime Ripard
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