linux-kernel - Re: [PATCH v5 2/6] media: sun6i: Add mod

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Message-ID: <20190107132929.ksyajmzn2gzr6oep@flea>
Date:   Mon, 7 Jan 2019 14:29:29 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     Yong Deng <yong.deng@...ewell.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        linux-media <linux-media@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-amarula@...rulasolutions.com,
        Michael Trimarchi <michael@...rulasolutions.com>
Subject: Re: [PATCH v5 2/6] media: sun6i: Add mod_rate quirk

On Mon, Dec 24, 2018 at 08:57:48PM +0530, Jagan Teki wrote:
> On Fri, Dec 21, 2018 at 6:30 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> >
> > On Thu, Dec 20, 2018 at 06:24:34PM +0530, Jagan Teki wrote:
> > > Unfortunately default CSI_SCLK rate cannot work properly to
> > > drive the connected sensor interface, particularly on few
> > > Allwinner SoC's like A64.
> > >
> > > So, add mod_rate quirk via driver data so-that the respective
> > > SoC's which require to alter the default mod clock rate can assign
> > > the operating clock rate.
> > >
> > > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > > ---
> > >  .../platform/sunxi/sun6i-csi/sun6i_csi.c      | 34 +++++++++++++++----
> > >  1 file changed, 28 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > index ee882b66a5ea..fe002beae09c 100644
> > > --- a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > +++ b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > @@ -15,6 +15,7 @@
> > >  #include <linux/ioctl.h>
> > >  #include <linux/module.h>
> > >  #include <linux/of.h>
> > > +#include <linux/of_device.h>
> > >  #include <linux/platform_device.h>
> > >  #include <linux/pm_runtime.h>
> > >  #include <linux/regmap.h>
> > > @@ -28,8 +29,13 @@
> > >
> > >  #define MODULE_NAME  "sun6i-csi"
> > >
> > > +struct sun6i_csi_variant {
> > > +     unsigned long                   mod_rate;
> > > +};
> > > +
> > >  struct sun6i_csi_dev {
> > >       struct sun6i_csi                csi;
> > > +     const struct sun6i_csi_variant  *variant;
> > >       struct device                   *dev;
> > >
> > >       struct regmap                   *regmap;
> > > @@ -822,33 +828,43 @@ static int sun6i_csi_resource_request(struct sun6i_csi_dev *sdev,
> > >               return PTR_ERR(sdev->clk_mod);
> > >       }
> > >
> > > +     if (sdev->variant->mod_rate)
> > > +             clk_set_rate_exclusive(sdev->clk_mod, sdev->variant->mod_rate);
> > > +
> >
> > It still doesn't make any sense to do it in the probe function...
> 
> I'm not sure we discussed about the context wrt probe, we discussed
> about exclusive put clock.

https://lkml.org/lkml/2018/12/18/584

"Doing it here is not really optimal either, since you'll put a
constraint on the system (maintaining that clock at 300MHz), while
it's not in use."

> Since clocks were enabling in set_power and clock rate can be set
> during probe in single time instead of setting it in set_power for
> every power enablement. anything wrong with that.

See above.

Plus, a clock running draws power. It doesn't really make sense to
draw power for something that is unused.

> > We discussed this in the previous iteration already.
> >
> > What we didn't discuss is the variant function that you introduce,
> > while the previous approach was enough.
> 
> We discussed about clk_rate_exclusive_put, and that even handle it in
> .remove right? so I have variant to handle it in sun6i_csi_remove.

We indeed discussed the clk_rate_exclusive_put. However, you chose to
implement it using a variant structure which really isn't needed.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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