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

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Date:	Mon, 11 Jul 2016 14:49:00 +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 2:45 PM, Vignesh R <vigneshr@...com> wrote:
>
>
> On Monday 11 July 2016 02:39 PM, prahlad venkata wrote:
>> On Mon, Jul 11, 2016 at 2:36 PM, prahlad venkata <prahlad.eee@...il.com> wrote:
>>> On Mon, Jul 11, 2016 at 2:14 PM, Vignesh R <vigneshr@...com> wrote:
>>>>
>>>>
>>>> On Monday 11 July 2016 01:34 PM, prahlad venkata wrote:
>>>>> 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;
>>>>
>>>> This is wrong. Deleting this line means QSPI_WR_SNGL is not set and no
>>>> data is sent out on the wire.
>>> QSPI_WR_SNGL is already set as soon as we enter the function.
>>>>
>>>>>>
>>>>>> 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.
>>>>
>>>> In qspi_write_msg(), qspi->cmd will always have WLEN set to
>>>> QSPI_WLEN(t->bits_per_word) and qspi->cmd is never changed within this
>>>> function.
>>>> It is the value of local variable 'cmd' that is changed to appropriate
>>>> WLEN (128bit or 8bit) as necessary.
>
>> 'cmd' is written back to qspi->cmd for every transaction.
>
> You mean qspi->cmd = cmd ?
> I don't see this happening anywhere in the driver. Can you point me to
> that line of code?
line 296:
ti_qspi_write(qspi, cmd, QSPI_SPI_CMD_REG);
if (ti_qspi_poll_wc(qspi)) {
    dev_err(qspi->dev, "write timed out\n");
    return -ETIMEDOUT;
 }


>
> --
> Regards
> Vignesh



-- 
Regards,
Prahlad.
+91-9663742838