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

[Icenowy Zheng]

在 2022-05-23星期一的 15:14 +0100，Peter Maydell写道：
> 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.

For the specific version on H3,
https://linux-sunxi.org/File:Allwinner_H3_Datasheet_V1.2.pdf .

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

Interesting, I will check it.

> -- PMM