mmc: t210: Fix 'bad' SD-card clock when doing 400KHz card detect

According to the HW team, for some reason the normal clock select code
picks what appears to be a perfectly valid 375KHz SD card clock, based
on the CAR clock source and SDMMC1 controller register settings (CAR =
408MHz PLLP0 divided by 68 for 6MHz, then a SD Clock Control register
divisor of 16 = 375KHz). But the resulting SD card clock, as measured by
the HW team, is 700KHz, which is out-of-spec. So the WAR is to use the
values given in the TRM PLLP table to generate a 400KHz SD-clock (CAR
clock of 24.7MHz, SD Clock Control divisor of 62) only for SDMMC1 on
T210 when the requested clock is <= 400KHz. Note that as far as I can
tell, the other requests for clocks in the Tegra MMC driver result in
valid SD clocks.

Signed-off-by: Tom Warren <twarren@nvidia.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/mmc/tegra_mmc.c b/drivers/mmc/tegra_mmc.c
index 73ac58c6c8d..2b041562a63 100644
--- a/drivers/mmc/tegra_mmc.c
+++ b/drivers/mmc/tegra_mmc.c
@@ -376,6 +376,25 @@ static void tegra_mmc_change_clock(struct tegra_mmc_priv *priv, uint clock)
 
 	rate = clk_set_rate(&priv->clk, clock);
 	div = (rate + clock - 1) / clock;
+
+#if defined(CONFIG_TEGRA210)
+	if (priv->mmc_id == PERIPH_ID_SDMMC1 && clock <= 400000) {
+		/* clock_adjust_periph_pll_div() chooses a 'bad' clock
+		 * on SDMMC1 T210, so skip it here and force a clock
+		 * that's been spec'd in the table in the TRM for
+		 * card-detect (400KHz).
+		 */
+		uint effective_rate = clock_adjust_periph_pll_div(priv->mmc_id,
+				CLOCK_ID_PERIPH, 24727273, NULL);
+		div = 62;
+
+		debug("%s: WAR: Using SDMMC1 clock of %u, div %d to achieve %dHz card clock ...\n",
+		      __func__, effective_rate, div, clock);
+	} else {
+		clock_adjust_periph_pll_div(priv->mmc_id, CLOCK_ID_PERIPH,
+					    clock, &div);
+	}
+#endif
 	debug("div = %d\n", div);
 
 	writew(0, &priv->reg->clkcon);