From: Conor Dooley <conor.dooley@microchip.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@microchip.com>
---
 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

On Wed, 12 Jun 2024 at 17:48, Conor Dooley <conor@kernel.org> wrote:
>
> From: Conor Dooley <conor.dooley@microchip.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@microchip.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
>

On Thu, Jun 20, 2024 at 02:50:15PM +0200, Ulf Hansson wrote:
> On Wed, 12 Jun 2024 at 17:48, Conor Dooley <conor@kernel.org> wrote:
> >
> > From: Conor Dooley <conor.dooley@microchip.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@microchip.com>
> 
> Looks reasonable to me. I assume you intend to send a non-RFC for
> this, that I can pick up?

I do intend doing that. How soon depends on whether or not you are
willing to take it on its own, or require it to come in a series with
the spi driver changes.

Thanks,
Conor.

On Thu, 20 Jun 2024 at 16:12, Conor Dooley <conor@kernel.org> wrote:
>
> On Thu, Jun 20, 2024 at 02:50:15PM +0200, Ulf Hansson wrote:
> > On Wed, 12 Jun 2024 at 17:48, Conor Dooley <conor@kernel.org> wrote:
> > >
> > > From: Conor Dooley <conor.dooley@microchip.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@microchip.com>
> >
> > Looks reasonable to me. I assume you intend to send a non-RFC for
> > this, that I can pick up?
>
> I do intend doing that. How soon depends on whether or not you are
> willing to take it on its own, or require it to come in a series with
> the spi driver changes.

I can pick it separately, if that makes sense to you.

Kind regards
Uffe