[PATCH] mmc: sdhci-msm: Warn about overclocking SD/MMC

[Douglas Anderson <dianders@chromium.org>]

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].

[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>
---

 drivers/mmc/host/sdhci-msm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
index 3451eb325513..dd41f6a4dbfb 100644
--- a/drivers/mmc/host/sdhci-msm.c
+++ b/drivers/mmc/host/sdhci-msm.c
@@ -353,6 +353,7 @@ 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 int achieved_rate;
 	int rc;
 
 	clock = msm_get_clock_rate_for_bus_mode(host, clock);
@@ -363,6 +364,17 @@ 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 %d 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),
-- 
2.29.2.576.ga3fc446d84-goog