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

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Message-ID: <20191103173227.GF7001@gilmour>
Date:   Sun, 3 Nov 2019 18:32:27 +0100
From:   Maxime Ripard <mripard@...nel.org>
To:     Jagan Teki <jagan@...rulasolutions.com>
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

On Fri, Nov 01, 2019 at 07:42:55PM +0530, Jagan Teki wrote:
> 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.

I guess we have two ways to go at this then.

Either we remove the return, but it might have a few side-effects, or
we call clk_get with NULL or bus depending on the case, and then call
regmap_mmio_attach_clk.

Maxime

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