[PATCH] mmc: sdhci-of-at91: fix set_uhs_signaling rewriting of MC1R

[Adrian Hunter]

On 30/06/22 12:09, Eugen Hristev wrote:
> In set_uhs_signaling, the DDR bit is being set by fully writing the MC1R
> register.
> This can lead to accidental erase of certain bits in this register.
> Avoid this by doing a read-modify-write operation.
> 
> Fixes: d0918764c17b ("mmc: sdhci-of-at91: fix MMC_DDR_52 timing selection")
> Signed-off-by: Eugen Hristev <eugen.hristev at microchip.com>
> Tested-by: Karl Olsen <karl at micro-technic.com>

Acked-by: Adrian Hunter <adrian.hunter at intel.com>

> ---
>  drivers/mmc/host/sdhci-of-at91.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-of-at91.c b/drivers/mmc/host/sdhci-of-at91.c
> index 10fb4cb2c731..cd0134580a90 100644
> --- a/drivers/mmc/host/sdhci-of-at91.c
> +++ b/drivers/mmc/host/sdhci-of-at91.c
> @@ -100,8 +100,13 @@ static void sdhci_at91_set_clock(struct sdhci_host *host, unsigned int clock)
>  static void sdhci_at91_set_uhs_signaling(struct sdhci_host *host,
>  					 unsigned int timing)
>  {
> -	if (timing == MMC_TIMING_MMC_DDR52)
> -		sdhci_writeb(host, SDMMC_MC1R_DDR, SDMMC_MC1R);
> +	u8 mc1r;
> +
> +	if (timing == MMC_TIMING_MMC_DDR52) {
> +		mc1r = sdhci_readb(host, SDMMC_MC1R);
> +		mc1r |= SDMMC_MC1R_DDR;
> +		sdhci_writeb(host, mc1r, SDMMC_MC1R);
> +	}
>  	sdhci_set_uhs_signaling(host, timing);
>  }
>