On Mon, May 30, 2022 at 11:22:26AM +0000, Conor.Dooley@xxxxxxxxxxxxx wrote:
> On 26/05/2022 19:13, Ivan Bornyakov wrote:
> > +static int mpf_read_status(struct spi_device *spi)
> > +{
> > + u8 status = 0, status_command = MPF_SPI_READ_STATUS;
> > + /*
> > + * Two identical SPI transfers are used for status reading.
> > + * The reason is that the first one can be inadequate.
> > + * We ignore it completely and use the second one.
> > + */
> > + struct spi_transfer xfers[] = {
> > + [0 ... 1] = {
> > + .tx_buf = &status_command,
> > + .rx_buf = &status,
> > + .len = 1,
> > + .cs_change = 1,
> > + }
> > + };
>
> Hmm, I don't think that this is correct, or at least it is not
> correct from the polarfire /soc/ perspective. I was told that
> there was nothing different other than the envm between the
> programming for both devices - but this is another situation
> where I start to question that.
>
> When I run this code, ISC enable /never/ passes - failing due
> to timing out. I see something like this picture here:
> https://i.imgur.com/EKhd1S3.png
> You can see the 0x0B ISC enable coming through & then a status
> check after it.
>
> With the current code, the value of the "status" variable will
> be 0x0, given you are overwriting the first MISO value with the
> second. According to the hw guys, the spi hw status *should*
> only be returned on MISO in the first byte after SS goes low.
>
> If this is not the case for a non -soc part, which, as I said
> before, I don't have a board with the SPI programmer exposed
> for & I have been told is not the case then my comments can
> just be ignored entirely & I'll have some head scratching to
> do...
>
> Thanks,
> Conor.
>
If I understood correctly, SS doesn't alter between two status reading
transactions despite .cs_change = 1. May be adding some .cs_change_delay
to spi_transfer struct can help with that?
> > + int ret = spi_sync_transfer(spi, xfers, 2);
> > +
> > + if ((status & MPF_STATUS_SPI_VIOLATION) ||
> > + (status & MPF_STATUS_SPI_ERROR))
> > + ret = -EIO;
> > +
> > + return ret ? : status;
> > +}
