On 4/6/23 10:37, Christoph Niedermaier wrote:
From: Marek Vasut [mailto:marex@xxxxxxx]
Sent: Wednesday, April 5, 2023 8:47 PM
On 4/5/23 20:24, Christoph Niedermaier wrote:
From: Marek Vasut [mailto:marex@xxxxxxx]
Sent: Wednesday, April 5, 2023 6:25 PM
On 4/5/23 18:02, Christoph Niedermaier wrote:
[...]
+/ {
+ model = "DH electronics i.MX6ULL DHCOR on maveo box";
+ compatible = "dh,imx6ull-dhcor-maveo-box", "dh,imx6ull-dhcor-som",
+ "fsl,imx6ull";
+
+ aliases {
+ /delete-property/ mmc0; /* Avoid double definitions */
+ /delete-property/ mmc1;
+ mmc2 = &usdhc2; /* eMMC should be mmc2 */
Why not mmc0 ?
Use root=PARTUUID= when booting to avoid any dependency on
root=/dev/mmcblk2pN enumeration.
This is due to software interchangeability with the DHCOM
i.MX6ULL, where the eMMC is always mmc2.
+CC Ulf , I vaguely recall some discussion about this enumeration and I
am not sure one can really depend on that.
That why I think it good to have a defined number for mmcblk devices
on an embedded system. An excerpt from [1]:
I might be misremembering this, but could it be that, if any non-OF
SDMMC controller probes early and hogs the /dev/mmcblk2 before the OF
ones have a chance to probe, then the OF ones would fail to probe ?
Alternative solutions like PARTUUIDs do not cover the case where multiple
mmcblk devices contain the same image.
I agree, this is indeed a downside of PARTUUID .
This is a common issue on devices
that can boot both from eMMC (for regular boot) and SD cards (as a
temporary boot medium for development). When a firmware image is
installed to eMMC after a test boot via SD card, there will be no
reliable way to refer to a specific device using (PART)UUIDs oder
LABELs
This can be solved by the installer updating the PARTUUID on the eMMC
however.
[1] https://patchwork.kernel.org/project/linux-mmc/patch/20200825134441.17537-2-matthias.schiffer@xxxxxxxxxxxxxxx/
So far I have never had a problem with numbering mmcblk devices via aliases.
Based on the above, I don't think either the aliases or PARTUUID is a
perfect solution, but the aliases should be fine for mx6ull at least?
So I think we can conclude this discussion thread ?
