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SubjectRe: [PATCH] [RFC] spi: pxa2xx: Do cs if restart the SSP during pxa2xx_spi_transfer_one()
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Hi

Is this also related to the regression with d5898e19c0d7 ("spi: pxa2xx:
Use core message processing loop") you have found or another issue?

Comments below.

On 3/7/19 9:24 AM, xiao jin wrote:
> The spi-pxa2xx can't read and write data correctly on our board.
> The pxa_ssp_type is LPSS_BXT_SSP in our case.
>
> With more debug we find that it's related to restart the SPP
> during pxa2xx_spi_transfer_one().
>
> In the normal case the spi_transfer_one_message() calls spi-pxa2xx
> cs_assert before transferring one message. After completing the
> transfer it calls spi-pxa2xx cs_deassert. The spi-pxa2xx works
> well.
>
> But in some other case pxa2xx_spi_unprepare_transfer() is called
> that clears SSCR0_SSE bit before the next transfer. In the next
> transfer the spi-pxa2xx driver will restart the SSP as the SSE
> bit is cleared. The cs_assert before the SSP restart can't ensure
> spi-pxa2xx work well.
>
> The patch is to do cs again if spi-pxa2xx restar the SSP during
> pxa2xx_spi_transfer_one()
>
Hmm.. please correct me if I'm wrong but pxa2xx_spi_unprepare_transfer()
is called always when there is no more messages pending and the spi core
should have deasserted the CS already?

More below.

> Signed-off-by: xiao jin <jin.xiao@intel.com>
> Signed-off-by: he, bo <bo.he@intel.com>
> ---
> drivers/spi/spi-pxa2xx.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
> index 14f4ea59caff..1a2ea46858d9 100644
> --- a/drivers/spi/spi-pxa2xx.c
> +++ b/drivers/spi/spi-pxa2xx.c
> @@ -928,6 +928,7 @@ static int pxa2xx_spi_transfer_one(struct spi_controller *master,
> u32 cr1;
> int err;
> int dma_mapped;
> + bool need_cs_change = false;
>
> /* Check if we can DMA this transfer */
> if (transfer->len > MAX_DMA_LEN && chip->enable_dma) {
> @@ -1056,6 +1057,11 @@ static int pxa2xx_spi_transfer_one(struct spi_controller *master,
> if ((pxa2xx_spi_read(drv_data, SSCR0) != cr0)
> || (pxa2xx_spi_read(drv_data, SSCR1) & change_mask)
> != (cr1 & change_mask)) {
> + /* It needs to deassert the chip selection
> + * firstly before restart the SPP */
> + need_cs_change = true;
> + cs_deassert(spi);
> +

I think code comes here at the beginning of each transfer so will be hit
multiple times before pxa2xx_spi_unprepare_transfer() if SPI message
consists of multiple transfers.

This makes me wondering if the device driver setting up the "struct
spi_transfer" is maybe missing the cs_change flag set for transfers
before last one in case HW needs CS toggling between transfers? For
instance what following drivers are doing with the cs_change flag:

drivers/char/tpm/tpm_tis_spi.c: tpm_tis_spi_transfer()
drivers/input/touchscreen/ad7877.c: ad7877_read(), ad7877_read_adc()

--
Jarkko

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