linux-kernel - Re: [PATCH v13 2/3] fpga: microchip-spi: add Microchip MPF FPGA manager

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Date:   Tue, 31 May 2022 17:01:22 +0300
From:   Ivan Bornyakov <i.bornyakov@...rotek.ru>
To:     Conor.Dooley@...rochip.com
Cc:     mdf@...nel.org, hao.wu@...el.com, yilun.xu@...el.com,
        trix@...hat.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-fpga@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        system@...rotek.ru
Subject: Re: [PATCH v13 2/3] fpga: microchip-spi: add Microchip MPF FPGA
 manager

On Tue, May 31, 2022 at 10:53:07AM +0000, Conor.Dooley@...rochip.com wrote:
> One last item, sorry!
> 
> On 30/05/2022 15:24, Conor Dooley wrote:
> > On 30/05/2022 13:07, Ivan Bornyakov wrote:
> >> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >>
> >> On Mon, May 30, 2022 at 11:22:26AM +0000, Conor.Dooley@...rochip.com 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,
> 
> Should cs_change be set for both messages or just the first?
>  From reading the documentation, it looks like we only want it
> for the first one.
> 
> https://elixir.bootlin.com/linux/latest/source/include/linux/spi/spi.h#L895
> 
> Thanks,
> Conor.
> 

You're right, I've overlooked that moment.

> >>>> +               }
> >>>> +       };
> >>>
> >>> 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?
> > 
> > D-oh - bug in the spi controller driver :)
> > LGTM now, successfully programmed my PolarFire SoC with v12.
> > I'd almost suggest adding a compatible for it too - but since
> > the envm programming doesn't work I don't think that would be
> > correct.
> > 
> > Tested-by: Conor Dooley <conor.dooley@...rochip.com>
> > 
> > With a small comment about why it's using spi_sync_transfer():
> > Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> > 
> >>
> >>>> +       int ret = spi_sync_transfer(spi, xfers, 2);
> >>>> +
> >>>> +       if ((status & MPF_STATUS_SPI_VIOLATION) ||
> >>>> +           (status & MPF_STATUS_SPI_ERROR))
> >>>> +               ret = -EIO;
> >>>> +
> >>>> +       return ret ? : status;
> >>>> +}
> >>
> > 
>