linux-kernel - Re: [PATCH v2] mmc: mmc_spi: allow for spi controllers incapable of getting as low as 400k

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Message-ID: <CAPDyKFoswLvgopz+cXCsxjZs4VRg-mrA66HTmfux57eY=--JMw@mail.gmail.com>
Date: Mon, 8 Jul 2024 14:23:47 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Conor Dooley <conor.dooley@...rochip.com>
Cc: linux-kernel@...r.kernel.org, conor@...nel.org, 
	Cyril Jean <cyril.jean@...rochip.com>, linux-mmc@...r.kernel.org
Subject: Re: [PATCH v2] mmc: mmc_spi: allow for spi controllers incapable of
 getting as low as 400k

On Tue, 25 Jun 2024 at 14:34, Conor Dooley <conor.dooley@...rochip.com> wrote:
>
> 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>

Applied for next, thanks!

Kind regards
Uffe


> ---
>
> Without the RFC tag, but otherwise unchanged.
>
> rfc/v1: https://lore.kernel.org/all/20240612-dense-resample-563f07c30185@spud/
>
> CC: Ulf Hansson <ulf.hansson@...aro.org>
> CC: Cyril Jean <cyril.jean@...rochip.com>
> CC: linux-mmc@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> ---
>  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 09d7a6a0dc1aa..c9caa1ece7ef9 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);
> --
> 2.43.2
>