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

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Date:	Mon, 11 Jul 2016 14:14:18 +0530
From:	Vignesh R <vigneshr@...com>
To:	prahlad venkata <prahlad.eee@...il.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 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->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.
So, as per you example, for the first 18 transactions(16*18 = 288bytes)
'cmd' variable will have WLEN field set to 0x7F(128bit). But for the
last 12 bytes, cmd is reinitialized to (that's the line being deleted
above):

cmd = qspi->cmd | QSPI_WR_SNGL;

which means WLEN field is set 1 byte.

So the below change won't be necessary. Or am I missing something?

>>
>>>                               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
Vignesh