linux-kernel - Re: [PATCH] spi: spi-ti-qspi: clear wlen field while setting word length.

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Date:	Mon, 11 Jul 2016 13:34:50 +0530
From:	prahlad venkata <prahlad.eee@...il.com>
To:	Vignesh R <vigneshr@...com>
Cc:	"broonie@...nel.org" <broonie@...nel.org>,
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] spi: spi-ti-qspi: clear wlen field while setting word length.

On Mon, Jul 11, 2016 at 10:37 AM, Vignesh R <vigneshr@...com> wrote:
> Hi Prahlad,
>
> On Sunday 10 July 2016 01:35 AM, Prahlad V wrote:
>> When a word length of 1 byte is selected and writing data of length
>> more than QSPI_WLEN_MAX_BYTES, first MAX_BYTES will be transfered
>> and remaining will be transfered byte by byte. In that case wlen
>> field should be cleared before setting.
>>
>> Signed-off-by: Prahlad V <prahlad.eee@...il.com>
>> ---
>>  drivers/spi/spi-ti-qspi.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/spi/spi-ti-qspi.c b/drivers/spi/spi-ti-qspi.c
>> index 29ea8d2..6c61f54 100644
>> --- a/drivers/spi/spi-ti-qspi.c
>> +++ b/drivers/spi/spi-ti-qspi.c
>> @@ -276,9 +276,9 @@ static int qspi_write_msg(struct ti_qspi *qspi, struct spi_transfer *t,
>>                               cmd |= QSPI_WLEN(QSPI_WLEN_MAX_BITS);
>>                       } else {
>>                               writeb(*txbuf, qspi->base + QSPI_SPI_DATA_REG);
>> -                             cmd = qspi->cmd | QSPI_WR_SNGL;
>
> qspi->cmd always has WLEN field cleared and set to WLEN = 1 byte (see
> ti_qspi_start_transfer_one()). And hence variable 'cmd' will also have
> WLEN set to 1 byte.
Even though WLEN=1 is set in the ti_qspi_transfer_one, if we ask for a
transfer of large data,
say 300 bytes in length, for attaining faster data rate WLEN 128 is
selected for the first two
transactions and remaining 44 bytes will be transmitted with WLEN 1.
During that case,
WLEN will be changed inside qspi_write_msg function itself and the
field should be cleared
first while doing that.
>
>>                               xfer_len = wlen;
>> -                             cmd |= QSPI_WLEN(wlen);
>> +                             cmd = ((qspi->cmd & ~QSPI_WLEN_MASK) |
>> +                                          QSPI_WLEN(wlen));
>
> So, this won't be necessary.
>
> --
> Regards
> Vignesh



-- 
Regards,
Prahlad.
+91-9663742838