Re: Issue with an SD-card switching to high speed

[Yann Gautier <yann.gautier@foss.st.com>]

On 10/19/22 17:50, Yann Gautier wrote:
> Hi Ulf (and mailing-list),
> 
> I've an SD-card on a STM32MP157F-DK2 board that cannot switch to 
> high-speed mode:
> "mmc0: Problem switching card into high-speed mode!"
> 
> On this board, it is not possible to switch to UHS modes.
> And there is no power cycle done in kernel.
> 
> When checking the differences when I add full-pwr-cycle in DT, I see 
> that the OCR we ask the card is different:
> 0x300000 (MMC_VDD_32_33 | MMC_VDD_33_34) vs 0x200000 (MMC_VDD_33_34).
> 
> If I add this missing MMC_VDD_32_33 voltage range (without power cycle), 
> then the card can switch to high-speed.
> 
> Checking where this is done in the framework, I've seen something that 
> could correct my issue in mmc_select_voltage():
> 
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 368f10405e13..bcd8fa81f78b 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1132,7 +1132,7 @@ u32 mmc_select_voltage(struct mmc_host *host, u32 
> ocr)
>                  mmc_power_cycle(host, ocr);
>          } else {
>                  bit = fls(ocr) - 1;
> -               ocr &= 3 << bit;
> +               ocr &= 3 << (bit - 1);
>                  if (bit != host->ios.vdd)
>                          dev_warn(mmc_dev(host), "exceeding card's 
> volts\n");
>          }
> 
> The ocr given to mmc_select_voltage() is 0x300000.
> fls(ocr) = 22, bit = 21, 3 << bit = 0x600000.
> With the &= operator, we then have only 0x200000 and have removed 
> MMC_VDD_32_33 mode.
> The architecture is an Armv7, I hope that the fls() has the same 
> behavior on other architectures.
> 
> But as this function is also used for eMMC and SDIO, this could have 
> impacts I've not seen.
> 
> 
> Maybe the issue is just with this SD-card, that doesn't properly handle 
> the range MMC_VDD_33_34 alone, and it could be out of spec.
> 
> I then have 3 possibilities:
> - stop using this type of card if it is out-of-specs
> - add full-pwr-cycle in this board's DT, but I'll have issues with other 
> boards that really cannot do power cycle
> - push the proposed patch in mmc_select_voltage()
> 
> 
> What's your opinion?
> 
> 
> 
> Best regards,
> Yann

Gentle ping.

Should I push the patch, and have the discussion based on that?


Thanks,
Yann