[PATCH 1/2] drm/tegra: Set the dsi lp clk parent and rate

[Sean Paul]

On Wed, Oct 8, 2014 at 8:11 AM, Peter De Schrijver
<pdeschrijver at nvidia.com> wrote:
> On Mon, Sep 22, 2014 at 12:11:54PM +0200, Thierry Reding wrote:
>> * PGP Signed by an unknown key
>>
>> On Mon, Sep 22, 2014 at 11:00:56AM +0200, Lucas Stach wrote:
>> > Am Freitag, den 19.09.2014, 15:53 -0400 schrieb Sean Paul:
>> > > Per NVidia, this clock rate should be around 70MHz in
>> > > order to properly sample reads on data lane 0. In order
>> > > to achieve this rate, we need to reparent the clock from
>> > > clk_m which can only achieve 12MHz. Add parent_lp to the
>> > > dts bindings and set the parent & rate on init.
>> > >
>> > > Signed-off-by: Sean Paul <seanpaul at chromium.org>
>> >
>> > NACK
>> >
>> > You are pushing SoC integration details into the binding of the device.
>> >
>> > You have two reasonable routes to go here: either the clock driver needs
>> > to be made smarter to reparent the clock in case the required clock rate
>> > could not be achieved with the current parent or you go the easy route
>> > and reparent the clock as part of the initial configuration.
>>
>> Agreed. There doesn't seem to be a case where it would make sense to
>> have this configurable per-board. Can you achieve the same effect by
>> adding this to the clock initialization table?
>>
>> Oh, I just see that we have this in the Tegra124 clock initialization
>> table:
>>
>>       {TEGRA114_CLK_DSIALP, TEGRA114_CLK_PLL_P, 68000000, 0},
>>       {TEGRA114_CLK_DSIBLP, TEGRA114_CLK_PLL_P, 68000000, 0},
>>
>> Doesn't that work for you already? If not that'd be a bug that should be
>> fixed in the clock driver.
>
> This seems the better approach indeed. Unless the rate would differ based
> on board or other external factors.
>

Thanks, Peter.

Just to close the loop, the patch: "clk: tegra124: Add init data for
dsi lp clocks" I sent up last week replaces this one.

Sean


> Cheers,
>
> Peter.