On 9/10/20 11:04 AM, Patrick DELAUNAY wrote:
Hi Alexandru,
Hi
[snip]
+ cfg->f_max = 52000000;
+ mmc_of_parse(dev, cfg);
Result of mmc_of_parse is not tested ?
I proposed:
+ ret = mmc_of_parse(dev, cfg);
+ if (ret)
+ return ret;
You're right. I'll get that updated.
I test this patch with a trace in stm32_sdmmc2_probe on STM32MP157C-EV1
[snip]
I think that it is a issue U-Boot, in mmc uclass in mmc_of_parse():
if (dev_read_bool(dev, "cap-mmc-highspeed"))
- cfg->host_caps |= MMC_CAP(MMC_HS);
+ cfg->host_caps |= MMC_CAP(MMC_HS) | MMC_CAP(MMC_HS_52);
In U-Boot this capability is splitted in 2 bits = one for 26MHz one for 52MHz
And for card side it is managed on card side by mmc_get_capabilities()
I agree. I am preparing a patch to address this.
[snip]
2) some host caps can be added in device tree (they are supported by SOC and by
Linux driver)
but they are not supported by U-Boot driver, for example:
#define MMC_MODE_DDR_52MHz MMC_CAP(MMC_DDR_52)
#define MMC_MODE_HS200 MMC_CAP(MMC_HS_200)
#define MMC_MODE_HS400 MMC_CAP(MMC_HS_400)
#define MMC_MODE_HS400_ES MMC_CAP(MMC_HS_400_ES)
I afraid (I don't sure) that this added caps change the mmc core behavior in
U-Boot =
U-Boot try to select the high speed mode even if not supported by driver....
Two issues here. The first is when devicetree enables an unsupported
mode, say "mmc-hs400-1_2v". That's a devicetree bug, and not something
we should fix in the code. Hypothetical exam: DT says
bus-width = <8>;
but only four lines are routed on the board.
The second issue is what happens when somebody plugs in a UHS SD card?
UHS support is not enabled by default in the stm32mp1 defconfigs, so the
mmc core won't try to run it at UHS.
Now if somebody were to enable UHS manually:
CONFIG_MMC_IO_VOLTAGE=y
CONFIG_MMC_UHS_SUPPORT=y
Then yes, the UHS switch will be attempted, fail, and the card will not
be detected.
To work around that, one could implement a .wait_dat0() that returns an
error other than -ENOSYS. This would cause mmc_switch_voltage() to fail,
making the mmc core to leave the card at default speeds.
My argument is that it takes conscious effort to break things in the
first place, so it's not a situation we should worry about.
The host_caps bitfield should be limited by the supported features in the
driver (or remove the unsupported features)
[snip]
cfg->host_caps &= SDMMC_SUPPORTED_CAPS;
or
cfg->host_caps |= ~SDMMC_UNSUPPORTED_CAPS;
I think this sort of playing with the flags will cause more confusion.
People would expect this to come from DT. For example, somebody sets
"sd-uhs-ddr52" in devicetree. It's more confusing to check host_caps,
and find that MMC_MODE_DDR_52MHz is not set than it is to see the driver
trying to place the card in DDR52 and failing.
Alex
