linux-kernel - RE: [PATCH v5 1/5] arm64/dts/qcom/sc7280: remove assigned-clock-rate property for mdp clk

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Date:   Fri, 11 Mar 2022 08:06:17 +0000
From:   Vinod Polimera <vpolimer@....qualcomm.com>
To:     Stephen Boyd <swboyd@...omium.org>,
        quic_vpolimer <quic_vpolimer@...cinc.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "dianders@...omium.org" <dianders@...omium.org>,
        quic_kalyant <quic_kalyant@...cinc.com>
Subject: RE: [PATCH v5 1/5] arm64/dts/qcom/sc7280: remove assigned-clock-rate
 property for mdp clk



> -----Original Message-----
> From: Stephen Boyd <swboyd@...omium.org>
> Sent: Wednesday, March 9, 2022 1:36 AM
> To: quic_vpolimer <quic_vpolimer@...cinc.com>;
> devicetree@...r.kernel.org; dri-devel@...ts.freedesktop.org;
> freedreno@...ts.freedesktop.org; linux-arm-msm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org; robdclark@...il.com;
> dianders@...omium.org; quic_kalyant <quic_kalyant@...cinc.com>
> Subject: Re: [PATCH v5 1/5] arm64/dts/qcom/sc7280: remove assigned-clock-
> rate property for mdp clk
> 
> WARNING: This email originated from outside of Qualcomm. Please be wary
> of any links or attachments, and do not enable macros.
> 
> Quoting Vinod Polimera (2022-03-08 08:54:56)
> > Kernel clock driver assumes that initial rate is the
> > max rate for that clock and was not allowing it to scale
> > beyond the assigned clock value.
> 
> How? I see ftbl_disp_cc_mdss_mdp_clk_src[] has multiple frequencies and
> clk_rcg2_shared_ops so it doesn't look like anything in the clk driver
> is preventing the frequency from changing beyond the assigned value.

Folowing the comment of Stephen, i have checked a bit more. it appears that clock driver is not setting the max clock from assgined clocks, dpu driver is doing that.
i am planning to fix it as below.
1) assign ULONG_MAX to max_rate while initializing clock in dpu driver.
2) remove unnecessary checks in the core_perf library. If rate doesn't match with the entries in the opp table, it will throw error, hence furthur checks are not needed.
3) no changes in dt are required. (we can drop all the posted ones)

Changes :
```--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
@@ -284,17 +284,6 @@ void dpu_core_perf_crtc_release_bw(struct drm_crtc *crtc)
 	}
 }
 
-static int _dpu_core_perf_set_core_clk_rate(struct dpu_kms *kms, u64 rate)
-{
-	struct dss_clk *core_clk = kms->perf.core_clk;
-
-	if (core_clk->max_rate && (rate > core_clk->max_rate))
-		rate = core_clk->max_rate;
-
-	core_clk->rate = rate;
-	return dev_pm_opp_set_rate(&kms->pdev->dev, core_clk->rate);
-}
-
 static u64 _dpu_core_perf_get_core_clk_rate(struct dpu_kms *kms)
 {
 	u64 clk_rate = kms->perf.perf_tune.min_core_clk;
@@ -405,7 +394,7 @@ int dpu_core_perf_crtc_update(struct drm_crtc *crtc,
 
 		trace_dpu_core_perf_update_clk(kms->dev, stop_req, clk_rate);
 
-		ret = _dpu_core_perf_set_core_clk_rate(kms, clk_rate);
+		ret = dev_pm_opp_set_rate(&kms->pdev->dev, clk_rate);
 		if (ret) {
 			DPU_ERROR("failed to set %s clock rate %llu\n",
 					kms->perf.core_clk->clk_name, clk_rate);
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_io_util.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_io_util.c
@@ -175,7 +175,7 @@ int msm_dss_parse_clock(struct platform_device *pdev,
 			continue;
 		mp->clk_config[i].rate = rate;
 		mp->clk_config[i].type = DSS_CLK_PCLK;
-		mp->clk_config[i].max_rate = rate;
+		mp->clk_config[i].max_rate = ULONG_MAX;
 	}
 
 	mp->num_clk = num_clk;
--```

Thanks,
Vinod.

> 
> >
> > Drop the assigned clock rate property and vote on the mdp clock as per
> > calculated value during the usecase.
> >
> > Changes in v2:
> > - Remove assigned-clock-rate property and set mdp clk during resume
> sequence.
> > - Add fixes tag.
> >
> > Changes in v3:
> > - Remove extra line after fixes tag.(Stephen Boyd)
> 
> This changelog should be removed.
> 
> >
> > Fixes: 62fbdce91("arm64: dts: qcom: sc7280: add display dt nodes")
> 
> I thought folks were saying that this is bad to keep? I don't really
> mind either way, but I guess it's better to drop the fixes tag because
> this is largely a performance improvement?
> 
> > Signed-off-by: Vinod Polimera <quic_vpolimer@...cinc.com>
> > Reviewed-by: Stephen Boyd <swboyd@...omium.org>