mmc: sdhci-of-at91: Implement specific ->set_clock() function

Disabling the internal clock while configuring the SD card clock can
lead to internal clock stabilization issue and/or unexpected switch to
the base clock when using presets.
A quirk SDHCI_QUIRK2_NEED_DELAY_AFTER_INT_CLK_RST was introduced to fix
these bugs. The cause was assumed to be a too long internal
re-synchronisation but it seems in some cases the delay (even if longer)
doesn't fix this bug. The safest workaround is to not disable/enable the
internal clock during the SD card clock configuration.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/drivers/mmc/host/sdhci-of-at91.c b/drivers/mmc/host/sdhci-of-at91.c
index 2703aa9..c1923c0 100644 (file)
--- a/drivers/mmc/host/sdhci-of-at91.c
+++ b/drivers/mmc/host/sdhci-of-at91.c
@@ -15,6 +15,7 @@
  */
 
 #include <linux/clk.h>
+#include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/io.h>
 #include <linux/mmc/host.h>
@@ -37,8 +38,52 @@ struct sdhci_at91_priv {
        struct clk *mainck;
 };
 
+static void sdhci_at91_set_clock(struct sdhci_host *host, unsigned int clock)
+{
+       u16 clk;
+       unsigned long timeout;
+
+       host->mmc->actual_clock = 0;
+
+       /*
+        * There is no requirement to disable the internal clock before
+        * changing the SD clock configuration. Moreover, disabling the
+        * internal clock, changing the configuration and re-enabling the
+        * internal clock causes some bugs. It can prevent to get the internal
+        * clock stable flag ready and an unexpected switch to the base clock
+        * when using presets.
+        */
+       clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+       clk &= SDHCI_CLOCK_INT_EN;
+       sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+       if (clock == 0)
+               return;
+
+       clk = sdhci_calc_clk(host, clock, &host->mmc->actual_clock);
+
+       clk |= SDHCI_CLOCK_INT_EN;
+       sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+       /* Wait max 20 ms */
+       timeout = 20;
+       while (!((clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL))
+               & SDHCI_CLOCK_INT_STABLE)) {
+               if (timeout == 0) {
+                       pr_err("%s: Internal clock never stabilised.\n",
+                              mmc_hostname(host->mmc));
+                       return;
+               }
+               timeout--;
+               mdelay(1);
+       }
+
+       clk |= SDHCI_CLOCK_CARD_EN;
+       sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+}
+
 static const struct sdhci_ops sdhci_at91_sama5d2_ops = {
-       .set_clock              = sdhci_set_clock,
+       .set_clock              = sdhci_at91_set_clock,
        .set_bus_width          = sdhci_set_bus_width,
        .reset                  = sdhci_reset,
        .set_uhs_signaling      = sdhci_set_uhs_signaling,
@@ -46,7 +91,6 @@ static const struct sdhci_ops sdhci_at91_sama5d2_ops = {
 
 static const struct sdhci_pltfm_data soc_data_sama5d2 = {
        .ops = &sdhci_at91_sama5d2_ops,
-       .quirks2 = SDHCI_QUIRK2_NEED_DELAY_AFTER_INT_CLK_RST,
 };
 
 static const struct of_device_id sdhci_at91_dt_match[] = {