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

From: Marc Gonzalez <marc.w.gonzalez@free.fr>
To: Heiner Kallweit <hkallweit1@gmail.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@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 11:20:14 +0100	[thread overview]
Message-ID: <b6971cd6-80f2-522a-64fb-82b126500010@free.fr> (raw)
In-Reply-To: <0696106f-8d70-6410-999a-fcda6c5b39c2@gmail.com>

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.

> 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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