Re: [Xen-devel] [PATCH 2 of 5] rombios/ata: Do not wait for BSY to be set

[Tim Deegan <tim@xxxxxxx>]

At 16:41 +0000 on 26 Nov (1353948093), Andrew Cooper wrote:
> I can't find any guarantee in the ATA specification that this will happen, 
> and it
> certainly does not with Qemu.  SeaBIOS has replaced it with a call to 
> udelay(5)
> instead.
> 
> As rombios does not have an equivalent udelay(), replace the wait with a write
> to port 0x80 which is whitelisted by Xen for 'a small delay'.

Does this actually do anything useful?  I'd guess that on qemu the extra
outb has no effect and on real hardware that needed a delay here, one
I/O cycle would not be enough.

Tim.

> This causes roughly 42k fewer traps to Qemu, which is very roughly 10% of the
> number of traps during boot of a Win7 guest.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> diff -r 1728fb789940 -r c223c044afbf tools/firmware/rombios/rombios.c
> --- a/tools/firmware/rombios/rombios.c
> +++ b/tools/firmware/rombios/rombios.c
> @@ -2914,8 +2914,8 @@ Bit16u device;
>  // 8.2.1 (a) -- set SRST in DC
>    outb(iobase2+ATA_CB_DC, ATA_CB_DC_HD15 | ATA_CB_DC_NIEN | ATA_CB_DC_SRST);
>  
> -// 8.2.1 (b) -- wait for BSY
> -  await_ide(BSY, iobase1, 20);
> +// 8.2.1 (b) -- wait
> +  outb(0x80, 0x00);
>  
>  // 8.2.1 (f) -- clear SRST
>    outb(iobase2+ATA_CB_DC, ATA_CB_DC_HD15 | ATA_CB_DC_NIEN);
> 
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