Hi,
On 23 May 2017 at 16:18, Andreas Färber afaerber@suse.de wrote:
Hi Heiko,
Am 23.05.2017 um 23:27 schrieb Heiko Stuebner:
Am Dienstag, 23. Mai 2017, 17:14:19 CEST schrieb Tom Rini:
On Tue, May 23, 2017 at 11:03:23PM +0200, Mark Kettenis wrote:
From: Heiko Stuebner heiko@sntech.de Date: Tue, 23 May 2017 22:29:33 +0200
Hi Kever, Tom,
Am Dienstag, 23. Mai 2017, 14:32:44 CEST schrieb Kever Yang:
This is not from kernel, seems the kernel mmc driver does notsupport aliases now,
thought I hope they both support the aliases for ordering.
there was a lengthy discussion about the pros and cons of ordering mmc devices last year [0].
With the outcome that explicit ordering via aliases is not desired and the argument being that mmc devices are not so different from usb storage or scsi/sata devices whose ordering is random all the time.
Aren't you intepreting the outcome of that discussion a bit too broadly tough? That discussion seems to reject an explicit ordering of mmc device names in the Linux kernel, mainly because better mechanisms exist to refer to a particular device than its device name/number. But that doesn't preclude having a meaningful set of aliases for certain boards if there is some sort of canonical boot order or if devices are actually numbered on a board?
In OpenFirmware the primary purpose of these aliases is to specify which device to boot from.
readding the lkml-link for the above: [0] https://lkml.org/lkml/2016/4/29/621
As for that being to broad, wasn't that why Tom suggested moving that to a -u-boot.dtsi file, because while generally not desired, it may benefit uboot to get some sane boot order / type marks (emmc, sd-card), but doesn't influence the core devicetree files that should ideally be synced from the kernel or wherever?
I think you're mixing three very distinct topics here: a) Whether Linux drivers should use aliases for ordering. b) Whether to add aliases in the DT. c) Sync'ing .dts files from Linux vs. local changes.
I don't see what's wrong with b) as it is useful as a shorthand for access to a particular node, e.g. for U-Boot's fdt commands.
Tom's point is that if a certain change is not in the Linux .dts and is needed for U-Boot, it should go into a U-Boot specific .dtsi file, so that the change doesn't get overwritten with the next .dts update from Linux. In the UEFI boot path we rely on a recent upstream-compatible DT being provided by U-Boot if none is installed by the OS in a way U-Boot can load, so the .dts will need to be re-sync'ed later on even if it doesn't affect U-Boot drivers. Therefore the commit messages also need to indicate where the .dts comes from, to avoid regressions on re-sync from different trees.
Further to that, I think U-Boot needs the aliases because we refer to devices by number.
At a future date if U-Boot moves away from this to named devices, we can revisit it.
But so far as I can tell, without the aliases, U-Boot cannot operate in a reliable, repeatable manner.
Regards, Simon