Re: [PATCH] hw/sd/allwinner-sdhost: report FIFO water level as 1 when data ready

[Peter Maydell]

On Fri, 20 May 2022 at 13:42, Icenowy Zheng <uwu@icenowy.me> wrote:
>
> U-Boot queries the FIFO water level to reduce checking status register
> when doing PIO SD card operation.
>
> Report a FIFO water level of 1 when data is ready, to prevent the code
> from trying to read 0 words from the FIFO each time.
>
> Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
> ---
>  hw/sd/allwinner-sdhost.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/hw/sd/allwinner-sdhost.c b/hw/sd/allwinner-sdhost.c
> index 041e45c680..b66fd9bce7 100644
> --- a/hw/sd/allwinner-sdhost.c
> +++ b/hw/sd/allwinner-sdhost.c
> @@ -114,7 +114,9 @@ enum {
>  };
>
>  enum {
> +    SD_STAR_FIFO_EMPTY      = (1 << 2),
>      SD_STAR_CARD_PRESENT    = (1 << 8),
> +    SD_STAR_FIFO_LEVEL_1    = (1 << 17),
>  };

Is there documentation on this hardware available somewhere?
The Linux kernel driver for it doesn't seem to have a #define
for this bit 17.

In an ideal world we'd actually emulate the FIFO itself
(our pl181 and bcm2835_sdhost models do this, for example).

-- PMM