linux-kernel - Re: [PATCH v11 4/7] drm/sun4i: dsi: Handle bus clock explicitly

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Message-ID: <CAMty3ZAWPZSHtAZDf_0Dpx588YGGv3pJX1cXMfkZus3+WF94cA@mail.gmail.com>
Date:   Fri, 1 Nov 2019 19:42:55 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <mripard@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-amarula <linux-amarula@...rulasolutions.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Icenowy Zheng <icenowy@...c.io>
Subject: Re: [PATCH v11 4/7] drm/sun4i: dsi: Handle bus clock explicitly

Hi Maxime,

On Tue, Oct 29, 2019 at 2:24 PM Maxime Ripard <mripard@...nel.org> wrote:
>
> On Tue, Oct 29, 2019 at 04:03:56AM +0530, Jagan Teki wrote:
> > > > explicit handling of common clock would require since the A64
> > > > doesn't need to mention the clock-names explicitly in dts since it
> > > > support only one bus clock.
> > > >
> > > > Also pass clk_id NULL instead "bus" to regmap clock init function
> > > > since the single clock variants no need to mention clock-names
> > > > explicitly.
> > >
> > > You don't need explicit clock handling. Passing NULL as the argument
> > > in regmap_init_mmio_clk will make it use the first clock, which is the
> > > bus clock.
> >
> > Indeed I tried that, since NULL clk_id wouldn't enable the bus clock
> > during regmap_mmio_gen_context code, passing NULL triggering vblank
> > timeout.
>
> There's a bunch of users of NULL in tree, so finding out why NULL
> doesn't work is the way forward.

I'd have looked the some of the users before checking the code as
well. As I said passing NULL clk_id to devm_regmap_init_mmio_clk =>
__devm_regmap_init_mmio_clk would return before processing the clock.

Here is the code snippet on the tree just to make sure I'm on the same
page or not.

static struct regmap_mmio_context *regmap_mmio_gen_context(struct device *dev,
                                        const char *clk_id,
                                        void __iomem *regs,
                                        const struct regmap_config *config)
{
        -----------------------
        --------------
        if (clk_id == NULL)
                return ctx;

        ctx->clk = clk_get(dev, clk_id);
        if (IS_ERR(ctx->clk)) {
                ret = PTR_ERR(ctx->clk);
                goto err_free;
        }

        ret = clk_prepare(ctx->clk);
        if (ret < 0) {
                clk_put(ctx->clk);
                goto err_free;
        }
        -------------
        ---------------
}

Yes, I did check on the driver in the tree before committing explicit
clock handle, which make similar requirements like us in [1]. this
imx2 wdt driver is handling the explicit clock as well. I'm sure this
driver is updated as I have seen few changes related to this driver in
ML.

Let me know if I still miss any key change or note here, I will dig
further on this for sure.

[1] https://elixir.bootlin.com/linux/v5.4-rc4/source/drivers/watchdog/imx2_wdt.c#L264

thanks,
Jagan.