Re: [PATCH 0/2] mmc: omap_hsmmc: Restore the init_stream sequence

[Peng Fan <peng.fan@oss.nxp.com>]

Hi Mathieu,

On Thu, Apr 10, 2025 at 11:00:19AM +0200, Mathieu Othacehe wrote:
>Hello,
>
>Back in 2019, the init_stream sequence was disabled with db52e19ced because:
>
>  This is not required. The MMC core sends CMD0 right after the
>  initialization and it serves the same purpose.
>
>That is wrong. It does not serve the same purpose at all. The init_stream
>function role is to keep the CMD line high for 74 clock cycles which is
>required by the SD specification[1]:
>
>  A device shall be ready to accept the first command within 1ms from detecting VDD min.
>  Device may use up to 74 clocks for preparation before receiving the first command.
>
>It turns out that one of the devices I am speaking to is requiring those 74
>clocks sequence before the send of the CMD0 as described in the specification.
>
>It was then broken since 2019.
>
>I guess that most of the other devices out there are able to cope with those
>74 clocks sequence missing and can respond directly to CMD0, which is why that
>went unnoticed with the omap_hsmmc driver users.

This patchset looks good to me.

Reviewd-by: Peng Fan <peng.fan@nxp.com>

But before apply the patchset. I would like see whether Jean has any
comments.

Thanks,
Peng

>
>I am proposing to restore that sequence, which is also used on the Linux side.
>
>Thanks,
>
>Mathieu
>
>[1]: https://academy.cba.mit.edu/classes/networking_communications/SD/SD.pdf
>
>Jean-Jacques Hiblot (1):
>  mmc: Add a new callback function to perform the 74 clocks cycle
>    sequence
>
>Mathieu Othacehe (1):
>  mmc: omap_hsmmc: implement send_init_stream callback
>
> drivers/mmc/mmc-uclass.c | 13 +++++++++++++
> drivers/mmc/mmc.c        |  6 ++++++
> drivers/mmc/omap_hsmmc.c | 13 +++++++++++--
> include/mmc.h            |  9 +++++++++
> 4 files changed, 39 insertions(+), 2 deletions(-)
>
>-- 
>2.47.1
>