linux-kernel - Re: [linux-sunxi] [PATCH 1/7] pinctrl: sunxi: add support for pin controllers without bus gate

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Date:   Thu, 11 Jan 2018 18:43:23 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     linux-sunxi@...glegroups.com, maxime.ripard@...e-electrons.com
Cc:     Andre Przywara <andre.przywara@....com>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-gpio@...r.kernel.org
Subject: Re: [linux-sunxi] [PATCH 1/7] pinctrl: sunxi: add support for pin controllers without bus gate

在 2018年1月11日星期四 CST 下午6:41:00，Maxime Ripard 写道：
> On Thu, Jan 11, 2018 at 10:23:52AM +0000, Andre Przywara wrote:
> > Hi,
> > 
> > On 11/01/18 10:14, Chen-Yu Tsai wrote:
> > > On Thu, Jan 11, 2018 at 6:08 PM, Andre Przywara <andre.przywara@....com> 
wrote:
> > >> Hi,
> > >> 
> > >> On 06/01/18 04:23, Icenowy Zheng wrote:
> > >>> The Allwinner H6 pin controllers (both the main one and the CPUs one)
> > >>> have no bus gate clocks.
> > >>> 
> > >>> Add support for this kind of pin controllers.
> > >>> 
> > >>> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
> > >>> ---
> > >>> 
> > >>>  drivers/pinctrl/sunxi/pinctrl-sunxi.c | 30
> > >>>  ++++++++++++++++++++----------
> > >>>  drivers/pinctrl/sunxi/pinctrl-sunxi.h |  1 +
> > >>>  2 files changed, 21 insertions(+), 10 deletions(-)
> > >>> 
> > >>> diff --git a/drivers/pinctrl/sunxi/pinctrl-sunxi.c
> > >>> b/drivers/pinctrl/sunxi/pinctrl-sunxi.c index
> > >>> 4b6cb25bc796..68cd505679d9 100644
> > >>> --- a/drivers/pinctrl/sunxi/pinctrl-sunxi.c
> > >>> +++ b/drivers/pinctrl/sunxi/pinctrl-sunxi.c
> > >>> @@ -1182,7 +1182,12 @@ static int sunxi_pinctrl_setup_debounce(struct
> > >>> sunxi_pinctrl *pctl,> >>> 
> > >>>       unsigned int hosc_div, losc_div;
> > >>>       struct clk *hosc, *losc;
> > >>>       u8 div, src;
> > >>> 
> > >>> -     int i, ret;
> > >>> +     int i, ret, clk_count;
> > >>> +
> > >>> +     if (pctl->desc->without_bus_gate)
> > >>> +             clk_count = 2;
> > >>> +     else
> > >>> +             clk_count = 3;
> > >>> 
> > >>>       /* Deal with old DTs that didn't have the oscillators */
> > >>>       if (of_count_phandle_with_args(node, "clocks", "#clock-cells")
> > >>>       != 3)
> > >>> 
> > >>> @@ -1360,15 +1365,19 @@ int sunxi_pinctrl_init_with_variant(struct
> > >>> platform_device *pdev,> >>> 
> > >>>                       goto gpiochip_error;
> > >>>       
> > >>>       }
> > >>> 
> > >>> -     clk = devm_clk_get(&pdev->dev, NULL);
> > >>> -     if (IS_ERR(clk)) {
> > >>> -             ret = PTR_ERR(clk);
> > >>> -             goto gpiochip_error;
> > >>> -     }
> > >>> +     if (!desc->without_bus_gate) {
> > >> 
> > >> Do we really need explicit support for that case?
> > >> Can't we have something that works automatically?
> > >> 
> > >> if (node has clock-names property)              (A)
> > >> 
> > >>         use clocks as enumerated and named there
> > > 
> > > You still need to know if the hardware has a bus gate or not.
> > > If it's missing, and it's disabled, you end up with unusable
> > > hardware.
> > 
> > Yes. So what? If you have a broken DT, it will not work. Just don't do
> > it. I don't understand why we want to defend against this case.
> 
> This is not the point, but rather: if we have a way to detect easily
> that the device tree is missing a property that is missing in our
> binding, why shouldn't we do it?
> 
> We're already doing it for reg and interrupts for example, why not for
> the clocks?
> 
> > > Unless you are fully trusting the device tree to be correct.
> > 
> > Sorry, but what else do we trust?
> > 
> > > IMHO that makes for hard to find bugs during SoC bringup.
> > 
> > I am not sure if that is really an issue. I would expect people
> > doing SoC bringup to be able to cope with those kinds of problems.
> 
> Riiiight, because it worked so well in the past. We definitely didn't
> overlooked some clocks used for debouncing in this particular driver,
> or some to get the timekeeping right in the RTC.
> 
> The argument that "anyone who codes in the kernel should just know
> better" doesn't work, on multiple levels. Because anyone that actually
> knows better can make a mistake or overlook some feature (because you
> didn't have your morning coffee yet, or because it was undocumented)
> and because you just make someone that doesn't feel bad.

I agree it here -- when I'm doing initial trial on H6 I didn't found that apb 
gate is missing ;-)

> 
> So, yes, we cannot not trust the device tree. But if we have a way to
> detect simple mistakes in the binding, we should also do it.
> 
> Maxime