mmc: bcm2835-mmc: Support underclocking

Support underclocking of the SD bus using the max-frequency DT property
(which currently has no DT parameter). The sd_overclock parameter
already provides another way to achieve the same thing which should be
equivalent in end result, but it is a bug not to support max-frequency
as well.

See: https://github.com/raspberrypi/linux/issues/2350

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

diff --git a/drivers/mmc/host/bcm2835-mmc.c b/drivers/mmc/host/bcm2835-mmc.c
index c4a5e992c6fb4a40b933239350ed4bfc8fb40155..b7f5fd96ecb6c59395022e868726f890ad3cd927 100644 (file)
--- a/drivers/mmc/host/bcm2835-mmc.c
+++ b/drivers/mmc/host/bcm2835-mmc.c
@@ -1310,8 +1310,8 @@ static int bcm2835_mmc_add_host(struct bcm2835_host *host)
 
        host->clk_mul = 0;
 
-       mmc->f_max = host->max_clk;
-       mmc->f_max = host->max_clk;
+       if (!mmc->f_max || mmc->f_max > host->max_clk)
+               mmc->f_max = host->max_clk;
        mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
 
        /* SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK */