[Freedreno] [PATCH v5 3/5] drm/msm/dp: set stream_pixel rate directly

[Stephen Boyd]

Quoting Dmitry Baryshkov (2022-04-19 09:34:18)
> On 08/03/2022 23:46, Stephen Boyd wrote:
> >
> > Yes that's my concern. The qmp phy driver has a couple clk_set_rate()
> > calls in the .configure_dp_phy callback. That is called from
> > phy_power_on() (see qcom_qmp_phy_power_on() and qcom_qmp_phy_dp_ops).
> > Looking at qcom_qmp_v3_phy_configure_dp_phy() it does
> >
> >          clk_set_rate(dp_clks->dp_link_hw.clk, dp_opts->link_rate * 100000);
> >          clk_set_rate(dp_clks->dp_pixel_hw.clk, pixel_freq);
> >
> > and I believe the child of dp_pixel_hw is find_clock("stream_pixel").
> > Looks like that is DISP_CC_MDSS_DP_PIXEL_CLK which is
> > disp_cc_mdss_dp_pixel_clk_src for the rate settable part. That has
> > clk_dp_ops which is clk_rcg2_dp_set_rate() for the set rate part. That
> > wants the parent clk frequency to be something non-zero to use in
> > rational_best_approximation(). If the clk_set_rate("stream_pixel") call
> > is made before phy_power_on() then the parent_rate in
> > clk_rcg2_dp_set_rate() won't be valid and the pixel clk frequency will
> > be wrong.
>
>
> Please excuse me, I didn't have time for this patchset up to now.

No worries. I lost this in my inbox!

>
> I double checked the previous patch (drm/msm/dp: "inline"
> dp_ctrl_set_clock_rate("ctrl_link")). Note, that the OPP is set _after_
> the PHY is powered on and configured.
>

Ok. If the clk_set_rate("stream_pixel") call is made after the
phy_power_on() then it should be equivalent.