Re: [PATCH] mmc: meson-gx: increase power-up delay

From: Jerome Brunet <jbrunet@baylibre.com>
To: Marc Gonzalez <marc.w.gonzalez@free.fr>,
	Heiner Kallweit <hkallweit1@gmail.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	Kevin Hilman <khilman@baylibre.com>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
	Pierre-Hugues Husson <phh@phh.me>,
	Rong Chen <rong.chen@amlogic.com>,
	Yang Yingliang <yangyingliang@huawei.com>
Cc: MMC <linux-mmc@vger.kernel.org>, AML <linux-amlogic@lists.infradead.org>
Subject: Re: [PATCH] mmc: meson-gx: increase power-up delay
Date: Wed, 15 Mar 2023 16:27:19 +0100	[thread overview]
Message-ID: <1jcz5axc8j.fsf@starbuckisacylon.baylibre.com> (raw)
In-Reply-To: <b6971cd6-80f2-522a-64fb-82b126500010@free.fr>

On Wed 15 Mar 2023 at 11:20, Marc Gonzalez <marc.w.gonzalez@free.fr> wrote:

> On 14/03/2023 20:45, Heiner Kallweit wrote:
>
>> On 14.03.2023 18:24, Marc Gonzalez wrote:
>> 
>>> With the default power-up delay, on small kernels, the host probes
>>> too soon, and mmc_send_io_op_cond() times out.
>> 
>> Looking at mmc_power_up() and how power_delay_ms is used
>> I wonder what you mean with "host probes too soon".
>
> Hello Heiner,
>
> Thanks for your interest in my patch! :)
>
> I should have added a link to the thread that led to the patch.
> https://patchwork.kernel.org/project/linux-wireless/patch/c1a215cf-94be-871b-2a8a-3cc381588f83@free.fr/
> Start at "I have run into another issue."
>
> Basically, I have an S905X2-based board.
> I built a small kernel for it (with only a few drivers), that boots really fast.
>
> mmc2 (SDIO controller hooked to WiFi chip) would not probe at all,
> unless I added lots of printks.
> Basically, calling mmc_send_io_op_cond() too soon after the controller
> has been reset leads to the CMD5 request timing out.
>
>

I tend to agree with Heiner here.
This patch is backing a contraint only reported on your design in the
driver of every AML SoC supported, for every MMC controller.

I think you should look first in your vmmc and vqmmc regulators and
their setup times.

"fixed-regulator" have properties which might be interesting to you,
like
 * startup-delay-us
 * off-on-delay-us

>> Are you sure that the additional delay is needed for the Amlogic MMC
>> block IP in general? Or could it be that your issue is caused by
>> a specific regulator and you need to add a delay there?
>
> The eternal question...
>
> I have only one type of board. (Actually, I have a reference design
> that is slightly different, so I should test on that one as well.)
>
> In vendor kernels, they add delays to the WiFi drivers.
> Maybe they have run into the issue, and they're just fixing the symptom?
>
> Default value for ios.power_delay_ms is 10 ms.
> msleep(ios.power_delay_ms) is called twice in mmc_power_up().
> So raising the delay from 10 to 20 adds 20 ms
> to the latency of initializing SDIO/SD/MMC controllers.
>
> Would you be willing to test if the problem manifests on your board?
>
> Regards

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