[PATCH 2/3] mmc: sdhci-iproc: Cap min clock frequency on BCM2711

[Stefan Wahren]

Hi Nicolas,

Am 06.04.21 um 12:48 schrieb Nicolas Saenz Julienne:
> There is a known bug on BCM2711's SDHCI core integration where the
> controller will hang when the difference between the core clock and the
> bus clock is too great. Specifically this can be reproduced under the
> following conditions:
>
> - No SD card plugged in, polling thread is running, probing cards at
>   100KHz.
> - BCM2711's core clock configured at 500MHz or more.
>
> So set 200MHz as the minimum clock frequency available for that board.
i think it should be 200 kHz?
>
> For more information on the issue see this:
> https://lore.kernel.org/linux-mmc/20210322185816.27582-1-nsaenz@kernel.org/T/#m11f2783a09b581da6b8a15f302625b43a6ecdeca
>
> Fixes: f84e411c85be ("mmc: sdhci-iproc: Add support for emmc2 of the BCM2711")
> Signed-off-by: Nicolas Saenz Julienne <nsaenz at kernel.org>
> ---
>  drivers/mmc/host/sdhci-iproc.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci-iproc.c b/drivers/mmc/host/sdhci-iproc.c
> index ddeaf8e1f72f..1ef888e91f73 100644
> --- a/drivers/mmc/host/sdhci-iproc.c
> +++ b/drivers/mmc/host/sdhci-iproc.c
> @@ -173,6 +173,23 @@ static unsigned int sdhci_iproc_get_max_clock(struct sdhci_host *host)
>  		return pltfm_host->clock;
>  }
>  
> +/*
> + * There is a known bug on BCM2711's SDHCI core integration where the
> + * controller will hang when the difference between the core clock and the bus
> + * clock is too great. Specifically this can be reproduced under the following
> + * conditions:
> + *
> + *  - No SD card plugged in, polling thread is running, probing cards at
> + *    100KHz.
> + *  - BCM2711's core clock configured at 500MHz or more
> + *
> + * So we set 200MHz as the minimum clock frequency available for that SoC.
> + */
> +static unsigned int sdhci_iproc_bcm2711_get_min_clock(struct sdhci_host *host)
> +{
> +	return 200000;
> +}
> +
>  static const struct sdhci_ops sdhci_iproc_ops = {
>  	.set_clock = sdhci_set_clock,
>  	.get_max_clock = sdhci_iproc_get_max_clock,
> @@ -271,6 +288,7 @@ static const struct sdhci_ops sdhci_iproc_bcm2711_ops = {
>  	.set_clock = sdhci_set_clock,
>  	.set_power = sdhci_set_power_and_bus_voltage,
>  	.get_max_clock = sdhci_iproc_get_max_clock,
> +	.get_min_clock = sdhci_iproc_bcm2711_get_min_clock,
>  	.set_bus_width = sdhci_set_bus_width,
>  	.reset = sdhci_reset,
>  	.set_uhs_signaling = sdhci_set_uhs_signaling,