linux-kernel - Re: [PATCH 5/7] mmc: meson-gx: avoid clock glitch when switching to DDR modes

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Date:   Thu, 18 Apr 2019 23:15:21 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        linux-amlogic@...ts.infradead.org, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] mmc: meson-gx: avoid clock glitch when switching to
 DDR modes

On Thu, 2019-04-18 at 22:53 +0200, Martin Blumenstingl wrote:
> Hi Jerome,
> 
> On Thu, Apr 18, 2019 at 10:46 PM Jerome Brunet <jbrunet@...libre.com> wrote:
> > On Thu, 2019-04-18 at 22:16 +0200, Martin Blumenstingl wrote:
> > > Hi Jerome,
> > > 
> > > On Wed, Apr 17, 2019 at 10:44 PM Jerome Brunet <jbrunet@...libre.com> wrote:
> > > > Activating DDR in the Amlogic mmc controller, among other things, will
> > > > divide the output clock by 2. So by activating it with clock on, we are
> > > > creating a glitch on the output.
> > > > 
> > > > Instead, let's deal with DDR when the clock output is off, when setting
> > > > the clock.
> > > > 
> > > > Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
> > > it seems that this patch breaks SD card on my Khadas VIM and Khadas VIM2.
> > 
> > The error I see in your logs is with eMMC and hs200, not SD card.
> sorry, I should have been more clear that there are two errors:
> eMMC, this is what I have been seeing for a while on my Khadas VIM2
> (it's probably not related to this patch):
>   mmc1: mmc_select_hs200 failed, error -84
>   mmc1: error -84 whilst initialising MMC card

Following patches were also supposed to help the vim2. 
... something I tested numerous time on this particular board.

> 
> however, then there's this other error:
>   print_req_error: I/O error, dev mmcblk0, sector 0 flags 0
>   Buffer I/O error on dev mmcblk0, logical block 0, async page read
> as result of this the partition table cannot be read and my kernel
> cannot find the rootfs.

I don't know what the problem is (probably some CRC error - you can check the log
in interrupt for this) but I'm pretty sure it is not related to this patch.

I see in the log SD is indeed in HS mode, so not in any DDR mode.
I also see that the SDIO fails as well. There something really weird, which can't
be explained by this patch alone AFAICT.

> 
> > Either way, There is something I don't really get. eMMC should not go through
> > any DDR mode to reach HS200 (which is an SDR mode), neither should SD to reach
> > HS.
> > 
> > All this does is flipping the DDR bit (when necessary) when clock if off for
> > the mmc device, avoiding a glitch on clk line.
> > 
> > This patch should not make any difference for SDR only setup, Maybe I missed
> > something, but I don't see how it could make anything different for SDR only.
> > 
> > I (repeatedly) tested both vim1 and vim2, without seeing this issue, so I can't
> > debug this. I'll need more detail to progress, something does not make sense here.
> please let me know from which part of the driver do you want debug logs
> 
> 
> Regards
> Martin