mmc0: unexpected command 5 error

[zougloub]

I'm plugging in a Pi 3 main µSD-card slot one BRCM43340 Wifi SDIO module which is working fine on my ThinkPad's SD/SDIO slot.

There are MMC issues, mmc0: unexpected command 5 error from drivers/mmc/host/bcm2835-sdhost.c (ping @pelwell) while the card is inserted.

I also made the system boot by USB to rule out the possibility of hot-plugging issues, same thing.

Running v4.8.y or v4.9.y (32-bit), and I'll try to build and troubleshoot, see if I can see something, but since my goal is to work with the wifi board, I'll probably quickly end up plugging it to another SoC.

[pelwell]

The SDHOST interface - the one that drives the SD card - is unlikely to work with an SDIO card because it turns off the SD clock between bus transactions.

[zougloub]

OK, good to know!

The other one (I have an MMC-HAT on the way), does it do SDIO?

[zougloub]

The interwebs says that yes, so I'm closing the issue. Thanks @pelwell for the prompt response.

[pelwell]

I'll give you a brief version of the whole story. The BCM2835 family of processors has two MMC/SD interfaces - mmc (also known as the Arasan block) is suitable for SDIO, sdhost isn't. There are 3 GPIO groups where mmc can be used (22-27, 34-39 and 48-53), and two for sdhost (34-39, 48-53); the SD slot (or EMMC) is on 48-53. We used to use mmc for everything (SD, uSD and EMMC) but then we switched to sdhost because a) it can be made quicker, and b) it frees up the SDIO-capable mmc. Then along comes the Pi3 and uses mmc to drive the WiFi chip via SDIO.

The assignment of mmc/sdhost interfaces to pins on the BCM2835 under Linux is controlled by Device Tree. Device Tree overlays can be used to change the group of pins used by each interface, and even force mmc to be used on the SD/uSD slot. This means that my first answer didn't give you the full picture. You could use a DT overlay to make mmc drive the uSD slot, which would make it SDIO capable, but then you would lose WiFi. Similarly, the MMC-HAT is capable of SDIO - it's just wiring pins 22-27 to the new uSD slot, which means it must be using mmc) but you won't also be able to use WiFi on the Pi3.

[zougloub]

I see. If I can't get the card to work on i.MX 6, I'll come back to the Pi and try to make a dtbo for my use case. Thanks again,

[pelwell]

The standard sdio overlay (which I've just simplified - https://github.com/raspberrypi/linux/blob/rpi-4.9.y/arch/arm/boot/dts/overlays/sdio-overlay.dts) ought to do what you want, or at least it should be a good starting point.

[zougloub]

(couldn't get my iMX6 board to underclock whereas the Pi3 is OK doing that with config.txt, so I'm back)

While I don't have the MMC-HAT, I tried the following, with the intent of routing mmc to the SD slot:

diff --git a/arch/arm/boot/dts/overlays/sdhost-overlay.dts b/arch/arm/boot/dts/overlays/sdhost-overlay.dts
index de3d1b0a5e40..305272b377b5 100644
--- a/arch/arm/boot/dts/overlays/sdhost-overlay.dts
+++ b/arch/arm/boot/dts/overlays/sdhost-overlay.dts
@@ -7 +7 @@
-       compatible = "brcm,bcm2708";
+       compatible = "brcm,bcm2837", "brcm,bcm2836";
diff --git a/arch/arm/boot/dts/overlays/sdio-overlay.dts b/arch/arm/boot/dts/overlays/sdio-overlay.dts
index 215d5e3e8a8c..28ded260878e 100644
--- a/arch/arm/boot/dts/overlays/sdio-overlay.dts
+++ b/arch/arm/boot/dts/overlays/sdio-overlay.dts
@@ -4 +4 @@
-/* Enable SDIO from MMC interface via GPIOs 22-27. Includes sdhost overlay. */
+/* Enable SDIO from MMC interface via GPIOs 48-53. Includes sdhost overlay. */
@@ -7 +7 @@
-       compatible = "brcm,bcm2708";
+       compatible = "brcm,bcm2837", "brcm,bcm2836";
@@ -25 +25 @@
-                               brcm,pins = <22 23 24 25 26 27>;
+                               brcm,pins = <48 49 50 51 52 53>;

but it looks like it's not doing anything (checked that /proc/device-tree/soc/gpio@*/sdio_pins/brcm,pins is indeed outputting the right values) to make the error go away ([ 231.776344] mmc0: unexpected command 5 error)

Did I do anything wrong?

[zougloub]

(reopening the issue, as there should be a way to get SDIO in the SD-card slot)

[pelwell]

Try dtoverlay=mmc.

[zougloub]

OK, I'll try to make it work and attach my dts.

[zougloub]

Cool, mmc-overlay.dtbs is working as it is.

Note that brcm.pull is brcm,pull in sdio-overlay.dtbs, I'm not sure how brcm,bcm2708 is still making it work, and IMHO adding comments to these overlays could be useful for those who aren't brute-forcing their way with web search engines.

[pelwell]

Thanks for spotting the typo - I've fixed that now. Using brcm,bcm2708 as the compatible string makes sense because that is the name of the family of SoCs, but in reality nothing is checking the string value.

Are you aware of the dtoverlay command in Raspbian? dtoverlay -a lists all known overlays, and dtoverlay -h <overlay> gives usage information for a named overlay. It reads /boot/overlays/README, so you may prefer to search it manually.