linux-kernel - Re: [PATCH] mmc: meson-mx-sdhc: Fix initialization frozen issue

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Date:   Mon, 3 Jul 2023 22:28:41 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Ziyang Huang <hzyitc@...look.com>
Cc:     ulf.hansson@...aro.org, neil.armstrong@...aro.org,
        khilman@...libre.com, jbrunet@...libre.com,
        linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: meson-mx-sdhc: Fix initialization frozen issue

Hello,

On Mon, Jun 19, 2023 at 9:51 PM Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:
>
> Hello,
>
> first of all: thank you for this patch!
>
> On Mon, Jun 19, 2023 at 7:36 PM Ziyang Huang <hzyitc@...look.com> wrote:
> >
> > Commit 4bc31edebde5 ("mmc: core: Set HS clock speed before sending
> > HS CMD13") set HS clock (52MHz) before switching to HS mode. For this
> > freq, FCLK_DIV5 will be selected and div value is 10 (reg value is 9).
> > Then we set rx_clk_phase to 11 or 15 which is out of range and make
> > hardware frozen. After we send command request, no irq will be
> > interrupted and the mmc driver will keep to wait for request finished,
> > even durning rebooting.
> I think this is the exact same problem I reported some days ago: [0]
> Ulf is questioning whether we properly support 52MHz clocks correctly,
> so I think you're onto something!
>
> So this is an excellent finding! I can confirm that using rx_clk_phase
> of 1 makes my Odroid-C1 eMMC work again :-)
>
> > So let's set a common value - 1 just for initialization. Then let
> > meson_mx_sdhc_execute_tuning() to find the accurate value for data
> > transfer.
> As far as I know unconditionally using value 1 can negatively affect
> other devices.
> I'm assuming that you're testing on an Odroid-C1 or similar board with
> HS200 eMMC:
> On those SoC + eMMC combinations we do support. But on other boards
> (for example Meson8b EC-100 / Endless Mini) there's no HS200 support
> because the eMMC is connected with 3.3V IO lines. So tuning is not
> executed there (if I recall correctly).
>
> What do you think about adding a special case for the 51MHz "actual
> clock rate" and adding a comment that it was found by manual testing?
> For some reason (that I don't understand) Amlogic's vendor driver
> maxes out at 47.22MHz (presumably because they limit themselves to
> using FCLK_DIV3 as input only - but I don't get why...).
Did you have the chance to look into my comment? I would like to hear
your opinion on this topic!


Best regards,
Martin