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

[<Conor.Dooley@microchip.com>]

On 30/05/2022 13:07, Ivan Bornyakov wrote:
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> On Mon, May 30, 2022 at 11:22:26AM +0000, Conor.Dooley@microchip.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,
>>> +               }
>>> +       };
>>
>> 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@microchip.com>

With a small comment about why it's using spi_sync_transfer():
Reviewed-by: Conor Dooley <conor.dooley@microchip.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;
>>> +}
>