Re: Applied "spi: pxa2xx: Deal with the leftover garbage in TXFIFO" to the spi tree

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Tue, Nov 13, 2018 at 8:37 PM Mark Brown <broonie@xxxxxxxxxx> wrote:

> There doesn't seem to be a way to empty TXFIFO on MMP2. The datasheet is
> super-secret and the method described in Armada 16x manual won't work:
>
>   "The TXFIFO and RXFIFO are cleared to 0b0 when the SSPx port is reset or
>   disabled (by writing a 0b0 to the <Synchronous Serial Port Enable> field
>   in the SSP Control Register 0)."
>
>   # devmem 0xd4037008           # read SSSR
>   0x0000F204
>   # devmem 0xd4037000 32 0x07   # SSE off in SSCR0
>   # devmem 0xd4037000 32 0x87   # SSE on
>   # devmem 0xd4037008
>   0x0000F204
>          ^ TXFIFO level is still 2. Sigh.
>
> The OLPC 1.75 boot firmware leaves two bytes in the TXFIFO. Those are
> basically throwaway bytes used in response to the messages from the EC.
> The OLPC kernel copes with this by power-cycling the hardware. Perhaps
> the firmware should do this instead.
>
> Other than that, there's not much we can do other than complain loudly
> until the garbage gets drained and discard the actual data... For the
> OLPC EC this will work just fine and pushing more data to TXFIFO would
> break further transactions.

> @@ -1078,6 +1078,20 @@ static int pxa2xx_spi_transfer_one(struct spi_controller *master,

Hmm...  Shouldn't be enough to do this in ->setup() or even in
->probe() / ->resume()?

-- 
With Best Regards,
Andy Shevchenko