mmc: sdhci-msm: Warn about overclocking SD/MMC

As talked about in commit 5e4b7e82d497 ("clk: qcom: gcc-sdm845: Use
floor ops for sdcc clks"), most clocks handled by the Qualcomm clock
drivers are rounded _up_ by default instead of down.  We should make
sure SD/MMC clocks are always rounded down in the clock drivers.
Let's add a warning in the Qualcomm SDHCI driver to help catch the
problem.

This would have saved a bunch of time [1].

NOTE: this doesn't actually fix any problems, it just makes it obvious
to devs that there is a problem and that should be an indication to
fix the clock driver.

[1] http://lore.kernel.org/r/20201210102234.1.I096779f219625148900fc984dd0084ed1ba87c7f@changeid

Suggested-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20201214092048.v5.1.Iec3430c7d3c2a29262695edef7b82a14aaa567e5@changeid
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
index 9c7927b..4d8dd70 100644 (file)
--- a/drivers/mmc/host/sdhci-msm.c
+++ b/drivers/mmc/host/sdhci-msm.c
@@ -352,6 +352,7 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
        struct sdhci_msm_host *msm_host = sdhci_pltfm_priv(pltfm_host);
        struct mmc_ios curr_ios = host->mmc->ios;
        struct clk *core_clk = msm_host->bulk_clks[0].clk;
+       unsigned long achieved_rate;
        int rc;
 
        clock = msm_get_clock_rate_for_bus_mode(host, clock);
@@ -362,10 +363,20 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
                       curr_ios.timing);
                return;
        }
+
+       /*
+        * Qualcomm clock drivers by default round clock _up_ if they can't
+        * make the requested rate.  This is not good for SD.  Yell if we
+        * encounter it.
+        */
+       achieved_rate = clk_get_rate(core_clk);
+       if (achieved_rate > clock)
+               pr_warn("%s: Card appears overclocked; req %u Hz, actual %lu Hz\n",
+                       mmc_hostname(host->mmc), clock, achieved_rate);
+
        msm_host->clk_rate = clock;
        pr_debug("%s: Setting clock at rate %lu at timing %d\n",
-                mmc_hostname(host->mmc), clk_get_rate(core_clk),
-                curr_ios.timing);
+                mmc_hostname(host->mmc), achieved_rate, curr_ios.timing);
 }
 
 /* Platform specific tuning */