linux-kernel - Re: [PATCH 4/4] mmc: mmci: add hs200 support for stm32 sdmmc

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Message-ID: <b7ef5887-ce9e-9ba1-5819-765e68104cc5@foss.st.com>
Date:   Thu, 16 Dec 2021 10:44:09 +0100
From:   Yann Gautier <yann.gautier@...s.st.com>
To:     Marek Vasut <marex@...x.de>, Ulf Hansson <ulf.hansson@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vladimir Zapolskiy <vz@...ia.com>,
        <u.kleine-koenig@...gutronix.de>,
        Christophe Kerello <christophe.kerello@...s.st.com>,
        Ludovic Barre <ludovic.barre@...s.st.com>,
        <linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 4/4] mmc: mmci: add hs200 support for stm32 sdmmc

On 12/16/21 10:14 AM, Marek Vasut wrote:
> On 12/15/21 15:17, Yann Gautier wrote:
>> Use feedback clock for HS200 mode, as for SDR104.
>> The HS200 mode can be enabled through DT by using mmc-hs200-1_8v.
>> It is possible to use it on STM32MP13, but not STM32MP15 platforms.
> 
> HS200 is possible even on the MP15, it just doesn't yield any 
> (performance) benefits due to the slower bus clock (125 MHz or so?), so 
> it isn't worth enabling it on MP15. It is nice to see MP13 can do better.

Hi Marek,

There is a limitation on MP15, please see errata sheet [1], chapter 2.3.19.
HS200 (and SDR104) shouldn't be enabled on MP15.

Best regards,
Yann

[1] https://www.st.com/resource/en/errata_sheet/dm00516256.pdf