RE: [PATCH] hw/ssi: imx_spi: Improve chip select handling

[Cheng, Xuzhou]

> > I got some free time in the past days to investigate this issue. Guenter is 
> > right, the Linux imx-spi driver does not work on QEMU.
> >
> > The reason is that the state of m25p80 machine loops in STATE_READING_DATA 
> > state after receiving RDSR command, the new command is ignored. Before 
> > sending a new command, the CS line should be pulled to high, this make the 
> > state of m25p80 back to IDLE.
> >
> > I have same point with Guenter, it's that set CS to 1 when burst is zero. 
> > But i don't think it is necessary to set CS to 0 in imx_spi_flush_txfifo(). 
> > I will send a new patch to fix this issue.
> >
> 
> Thanks a lot for looking into this. If you have a better solution than mine, 
> by all means, please go for it. As I mentioned in my patch, I didn't really 
> like it, but I was unable to find a better solution.
I am doing some experiment to verify that the new patch is reasonable, so the 
new patch will be delayed few days.

> 
> > BTW, the Linux driver uses DMA mode when transfer length is greater than 
> > the FIFO size, But QEMU imx-spi model doesn't support DMA now.
> 
> Does it have practical impact ? Obviously my tests were somewhat limited (I 
> was happy to get Linux booting from flash), but I don't recall seeing a 
> problem.
There seem have no practical impact. :)