Re: [PATCH 1/2] hw/ssi: imx_spi: Correct the burst length > 32 bit transfer logic

[Bin Meng]

On Thu, Dec 31, 2020 at 6:31 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 12/17/20 6:28 AM, Bin Meng wrote:
> > From: Bin Meng <bin.meng@windriver.com>
> >
> > For the ECSPIx_CONREG register BURST_LENGTH field, the manual says:
> >
> > 0x020 A SPI burst contains the 1 LSB in first word and all 32 bits in 
> > second word.
> > 0x021 A SPI burst contains the 2 LSB in first word and all 32 bits in 
> > second word.
> >
> > Current logic uses either s->burst_length or 32, whichever smaller,
> > to determine how many bits it should read from the tx fifo each time.
> > For example, for a 48 bit burst length, current logic transfers the
> > first 32 bit from the first word in the tx fifo, followed by a 16
> > bit from the second word in the tx fifo, which is wrong. The correct
> > logic should be: transfer the first 16 bit from the first word in
> > the tx fifo, followed by a 32 bit from the second word in the tx fifo.
> >
> > With this change, SPI flash can be successfully probed by U-Boot on
> > imx6 sabrelite board.
> >
> >   => sf probe
> >   SF: Detected sst25vf016b with page size 256 Bytes, erase size 4 KiB, 
> > total 2 MiB
> >
> > Fixes: c906a3a01582 ("i.MX: Add the Freescale SPI Controller")
> > Signed-off-by: Bin Meng <bin.meng@windriver.com>
> > ---
> >
> >  hw/ssi/imx_spi.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/ssi/imx_spi.c b/hw/ssi/imx_spi.c
> > index 85c172e..509fb9f 100644
> > --- a/hw/ssi/imx_spi.c
> > +++ b/hw/ssi/imx_spi.c
> > @@ -178,7 +178,10 @@ static void imx_spi_flush_txfifo(IMXSPIState *s)
> >
> >          DPRINTF("data tx:0x%08x\n", tx);
> >
> > -        tx_burst = MIN(s->burst_length, 32);
> > +        tx_burst = s->burst_length % 32;
> > +        if (tx_burst == 0) {
> > +            tx_burst = 32;
> > +        }
>
> Or alternatively using ternary operator:
>
>            tx_burst = (s->burst_length % 32) ?: 32;

Updated this in v2 series:
http://patchwork.ozlabs.org/project/qemu-devel/list/?series=222931

>
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>

Regards,
Bin