Re: Accessing MMC/SD card storage on Raspberry Pi

["Tomaž Šolc" <tomaz.solc@klevio.com>]

Hi

On 12. 02. 19 12:22, Roland Hieber wrote:
> If I remember correctly, there was a patch changing that behaviour... Ah
> yes, commit abc0447440d6 [0]:
> 
>      ARM: dts: bcm2835-rpi: re-enable booting from SD card
> 
>      Kernel commit a19adf8d86e822eba502486524127595372c85f6 [0] changed the
>      RPi1 device tree from &sdhci to &sdhost, which was imported in barebox
>      commit d14b844b08635c717fb52a294ed8d6872e260315. It seems that barebox
>      does not have a driver for brcm,bcm2835-sdhost (yet), which resulted in
>      barebox unable to boot from SD card. However, the driver for
>      brcm,bcm2835-sdhci worked fine in the past.
> 
>      Although the upstream change was made for good reasons, the simplest
>      change for barebox for now is to revert to using &sdhci and disable
>      &sdhost.
> 
> [0]: https://git.pengutronix.de/cgit/barebox/commit/?h=master&id=abc0447440d6
> 
> The "solution" was a small device tree fix. Could this be related to
> your problem? Unfortunately no one here has a RPi Compute Module, but
> there were already similar questions in the last month. (Cc Moritz)

Ah, thanks for pointing this out. That commit only touched device tree 
for R.Pi 1. I tried to do something similar on Compute Module 3 by 
adding the following into bcm2837-rpi-3.dts:

&sdhci {
	pinctrl-0 = <&emmc_gpio48>;
	/delete-property/ mmc-pwrseq;
	/delete-property/ non-removable;
	/delete-property/ #address-cells;
	/delete-property/ #size-cells;
	/delete-node/ wifi@1;
};

&sdhost {
	status = "disabled";
};

Unfortunately it fails to boot like that with the last things printed 
out being:

initcall-> rpi_devices_init+0x0/0x138
register_device: bcm2835_fb0
bcm2835_mci 3f300000.sdhci@7e300000.of: Wanted 400000 hz, returning 
divider 313 (626) which yields 399361 hz
bcm2835_mci 3f300000.sdhci@7e300000.of: Changing bus width to 1
bcm2835_mci 3f300000.sdhci@7e300000.of: IO settings: bus width=0, 
frequency=400000 Hz
bcm2835_mci 3f300000.sdhci@7e300000.of: Changing bus width to 1
bcm2835_mci 3f300000.sdhci@7e300000.of: IO settings: bus width=0, 
frequency=400000 Hz

One possible reason for this might be that pin functions aren't 
re-assigned. I think pinctrl isn't implemented for bcm2835. It probably 
works on R.Pi 1 because there firmware already assigns correct pin 
functions by default before jumping to Bearbox.

I'll see if I can implement pinctrl. It shouldn't be much work since 
most things already seem to be implemented in gpio-bcm2835.c.

Best regards
Tomaž

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