[U-Boot] [PATCH 10/14] dm: mmc: sunxi: Add support for driver model

[Suneel Garapati]

Hi Simon,

I have similar requirement of Cavium boards using two card slots on
one host and currently trying to figure out to support it using
DM_MMC.
Would like to know if you have quick thoughts or seen similar use case
with some other boards too?

Please correct me if I miss something obvious.

Regards,
Suneel


On Thu, Jul 27, 2017 at 9:19 PM, Simon Glass <sjg at chromium.org> wrote:
> Hi Maxime,
>
> On 17 July 2017 at 03:26, Maxime Ripard
> <maxime.ripard at free-electrons.com> wrote:
>> Hi Simon,
>>
>> On Fri, Jul 14, 2017 at 07:47:45AM -0600, Simon Glass wrote:
>>> On 5 July 2017 at 14:14, Maxime Ripard <maxime.ripard at free-electrons.com> wrote:
>>> > On Wed, Jul 05, 2017 at 04:57:40PM +0200, Maxime Ripard wrote:
>>> >> On Tue, Jul 04, 2017 at 01:33:25PM -0600, Simon Glass wrote:
>>> >> > Hi Maxime,
>>> >> >
>>> >> > On 21 June 2017 at 01:31, Maxime Ripard
>>> >> > <maxime.ripard at free-electrons.com> wrote:
>>> >> > > Hi Simon,
>>> >> > >
>>> >> > > On Mon, Jun 19, 2017 at 11:11:27AM -0600, Simon Glass wrote:
>>> >> > >> Add a driver-model version of this driver which mostly uses the existing
>>> >> > >> code. The old code can be removed once all boards are switched over.
>>> >> > >>
>>> >> > >> Signed-off-by: Simon Glass <sjg at chromium.org>
>>> >> > >
>>> >> > > I'm not sure if you tested that, but we have some code that switches
>>> >> > > the MMC indices when using both an eMMC and an external MMC.
>>> >> > >
>>> >> > > http://git.denx.de/?p=u-boot.git;a=blob;f=board/sunxi/board.c#l494
>>> >> > >
>>> >> > > This predates my time, but it seems that it was done to have a
>>> >> > > consistent boot MMC device ID.
>>> >> > >
>>> >> > > I'm not really sure we can get rid of it (even if it creates some
>>> >> > > issues of it's own), but what would be the impact of a switch to the
>>> >> > > device model on that logic?
>>> >> >
>>> >> > That is a pretty terrible hack.
>>> >>
>>> >> Yes, I know. This is especially bad when used together with other
>>> >> tools that rely on one MMC index for example (such as fastboot).
>>> >>
>>> >> I wanted to kill it for quite some time, but I'm a bit reluctant due
>>> >> to the possible side effects.
>>> >>
>>> >> > I'm not sure whether it will continue to work with DM. It does still
>>> >> > use the device number in the block device, so maybe...  Do you have
>>> >> > a board would use this?
>>> >>
>>> >> I guess I do. I'll give it a try or tonight and let you know.
>>> >
>>> > I just tested. Even with an eMMC (which was the first use case for
>>> > that hack), it works, even things that are not mainline yet (fastboot,
>>> > etc).
>>> >
>>> > It obviously break the old scripts relying on the mmc index, but I
>>> > guess that's ok.
>>> >
>>> > There's one regression though. Our eMMC will always be the second one,
>>> > which means that the distro bootargs will always boot on the external
>>> > SD first (which is always going to be mmc0).
>>> >
>>> > That's due to the fact that the eMMC controller is the third one, and
>>> > is thus probed last. We obviously want something deterministic for
>>> > fastboot for example, but booting partitions of the media you started
>>> > from make sense I guess. And this is what this hack was trying to
>>> > address.
>>>
>>> OK...so what should we do here?
>>
>> I guess we should just drop the hack. We'll have to at some point
>> anyway. But I guess we should also find a way to tweak the distro
>> bootcmd at boot time to search for the medium that we booted on first.
>>
>> I'm not really sure how to do this though.
>
> Well in that case let's drop the hack and someone will pick it up when
> it hits them.
>
> Regards,
> Simon
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