linux-kernel - Re: [PATCH v4 3/6] media: sun6i: Update default CSI

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Date:   Wed, 19 Dec 2018 11:07:38 +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 v4 3/6] media: sun6i: Update default CSI_SCLK for A64

On Tue, Dec 18, 2018 at 09:08:17PM +0530, Jagan Teki wrote:
> On Tue, Dec 18, 2018 at 8:53 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> >
> > On Tue, Dec 18, 2018 at 05:03:17PM +0530, Jagan Teki wrote:
> > > Unfortunately A64 CSI cannot work with default CSI_SCLK rate.
> > >
> > > A64 BSP is using 300MHz clock rate as default csi clock,
> > > so sun6i_csi require explicit change to update CSI_SCLK
> > > rate to 300MHZ for A64 SoC's.
> > >
> > > So, set the clk_mod to 300MHz only for A64.
> > >
> > > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > > ---
> > >  drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > index 9ff61896e4bb..91470edf7581 100644
> > > --- a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > +++ b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > @@ -822,6 +822,11 @@ static int sun6i_csi_resource_request(struct sun6i_csi_dev *sdev,
> > >               return PTR_ERR(sdev->clk_mod);
> > >       }
> > >
> > > +     /* A64 require 300MHz mod clock to operate properly */
> > > +     if (of_device_is_compatible(pdev->dev.of_node,
> > > +                                 "allwinner,sun50i-a64-csi"))
> > > +             clk_set_rate_exclusive(sdev->clk_mod, 300000000);
> > > +
> >
> > If you're using clk_set_rate_exclusive, you need to put back the
> > "exclusive" reference once you're not using the clock.
> >
> > 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.
> 
> I think we can handle via clk_rate_exclusive_put for those errors
> cases? If I'm not wrong

Yes, but it's not only for the error case, it's also for the inactive
case.

Maxime

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

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