linux-kernel - Re: [RFC v1 1/3] mmc: mmc_spi: allow for spi controllers incapable of getting as low as 400k

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Message-ID: <CAPDyKFozcUPuMooDHVSBZomHTGKzseVf9F=YBY_uQejh9o3x7g@mail.gmail.com>
Date: Thu, 20 Jun 2024 14:50:15 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Conor Dooley <conor@...nel.org>
Cc: linux-mmc@...r.kernel.org, Conor Dooley <conor.dooley@...rochip.com>, 
	cyril.jean@...rochip.com, Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [RFC v1 1/3] mmc: mmc_spi: allow for spi controllers incapable of
 getting as low as 400k

On Wed, 12 Jun 2024 at 17:48, Conor Dooley <conor@...nel.org> wrote:
>
> From: Conor Dooley <conor.dooley@...rochip.com>
>
> Some controllers may not be able to reach a bus clock as low as 400 KHz
> due to a lack of sufficient divisors. In these cases, the SD card slot
> becomes non-functional as Linux continuously attempts to set the bus
> clock to 400 KHz. If the controller is incapable of getting that low,
> set its minimum frequency instead. While this may eliminate some SD
> cards, it allows those capable of operating at the controller's minimum
> frequency to be used.
>
> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>

Looks reasonable to me. I assume you intend to send a non-RFC for
this, that I can pick up?

Kind regards
Uffe

> ---
>  drivers/mmc/host/mmc_spi.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
> index 09d7a6a0dc1a..c9caa1ece7ef 100644
> --- a/drivers/mmc/host/mmc_spi.c
> +++ b/drivers/mmc/host/mmc_spi.c
> @@ -1208,7 +1208,10 @@ static int mmc_spi_probe(struct spi_device *spi)
>          * that's the only reason not to use a few MHz for f_min (until
>          * the upper layer reads the target frequency from the CSD).
>          */
> -       mmc->f_min = 400000;
> +       if (spi->controller->min_speed_hz > 400000)
> +               dev_warn(&spi->dev,"Controller unable to reduce bus clock to 400 KHz\n");
> +
> +       mmc->f_min = max(spi->controller->min_speed_hz, 400000);
>         mmc->f_max = spi->max_speed_hz;
>
>         host = mmc_priv(mmc);
> --
> 2.43.0
>