mmc: jz4740: Work around bug on JZ4760(B)

commit 3f18c5046e633cc4bbad396b74c05d46d353033d upstream.

On JZ4760 and JZ4760B, SD cards fail to run if the maximum clock
rate is set to 50 MHz, even though the controller officially does
support it.

Until the actual bug is found and fixed, limit the maximum clock rate to
24 MHz.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230131210229.68129-1-paul@crapouillou.net
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/mmc/host/jz4740_mmc.c b/drivers/mmc/host/jz4740_mmc.c
index 3c59dec08c3bdd15ebdc562911efec0c6f741239..8586447d4b4f26b54b6cbf3b9da6f5c177aa6f05 100644 (file)
--- a/drivers/mmc/host/jz4740_mmc.c
+++ b/drivers/mmc/host/jz4740_mmc.c
@@ -1038,6 +1038,16 @@ static int jz4740_mmc_probe(struct platform_device* pdev)
        mmc->ops = &jz4740_mmc_ops;
        if (!mmc->f_max)
                mmc->f_max = JZ_MMC_CLK_RATE;
+
+       /*
+        * There seems to be a problem with this driver on the JZ4760 and
+        * JZ4760B SoCs. There, when using the maximum rate supported (50 MHz),
+        * the communication fails with many SD cards.
+        * Until this bug is sorted out, limit the maximum rate to 24 MHz.
+        */
+       if (host->version == JZ_MMC_JZ4760 && mmc->f_max > JZ_MMC_CLK_RATE)
+               mmc->f_max = JZ_MMC_CLK_RATE;
+
        mmc->f_min = mmc->f_max / 128;
        mmc->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;