On Tue, Sep 13, 2022 at 06:40:10PM -0700, Brian Norris wrote:
> This loop intends to retry a max of 10 times, with some implicit
> termination based on the SD_{R,}OCR_S18A bit. Unfortunately, the
> termination condition depends on the value reported by the SD card
> (*rocr), which may or may not correctly reflect what we asked it to do.
>
> Needless to say, it's not wise to rely on the card doing what we expect;
> we should at least terminate the loop regardless. So, check both the
> input and output values, so we ensure we will terminate regardless of
> the SD card behavior.
>
> Note that SDIO learned a similar retry loop in commit 0797e5f1453b
> ("mmc: core: Fixup signal voltage switch"), but that used the 'ocr'
> result, and so the current pre-terminating condition looks like:
>
> rocr & ocr & R4_18V_PRESENT
>
> (i.e., it doesn't have the same bug.)
>
> This addresses a number of crash reports seen on ChromeOS that look
> like the following:
>
> ... // lots of repeated: ...
> <4>[13142.846061] mmc1: Skipping voltage switch
> <4>[13143.406087] mmc1: Skipping voltage switch
> <4>[13143.964724] mmc1: Skipping voltage switch
> <4>[13144.526089] mmc1: Skipping voltage switch
> <4>[13145.086088] mmc1: Skipping voltage switch
> <4>[13145.645941] mmc1: Skipping voltage switch
> <3>[13146.153969] INFO: task halt:30352 blocked for more than 122 seconds.
> ...
>
> Fixes: f2119df6b764 mmc: sd: add support for signal voltage switch procedure
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
>
> drivers/mmc/core/sd.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> index 06aa62ce0ed1..3662bf5320ce 100644
> --- a/drivers/mmc/core/sd.c
> +++ b/drivers/mmc/core/sd.c
> @@ -870,7 +870,8 @@ int mmc_sd_get_cid(struct mmc_host *host, u32 ocr, u32 *cid, u32 *rocr)
> * the CCS bit is set as well. We deliberately deviate from the spec in
> * regards to this, which allows UHS-I to be supported for SDSC cards.
> */
> - if (!mmc_host_is_spi(host) && rocr && (*rocr & SD_ROCR_S18A)) {
> + if (!mmc_host_is_spi(host) && (ocr & SD_OCR_S18R) &&
> + rocr && (*rocr & SD_ROCR_S18A)) {
> err = mmc_set_uhs_voltage(host, pocr);
> if (err == -EAGAIN) {
> retries--;
> --
> 2.37.2.789.g6183377224-goog
>
