[U-Boot] [PATCH] mx28: fix i.MX28 spi driver

[Matthias Fuchs]

On 01/14/2012 03:10 PM, Marek Vasut wrote:
>> The generic spi flash driver (drivers/mtd/spi/spi_flash.c) uses the
>> spi low level driver's spi_xfer() function with len=0 to deassert the
>> SPI flash' chip select. But the i.MX28 spi driver rejects this call
>> due to len=0.
>>
>> This patch implements an exception for len=0 with the SPI_XFER_END
>> flag set. This results in an extra read with the chip select being
>> deasserted afterwards. There seems to be no way to deassert the signal
>> by hand.
> 
> This seems good, but it doesn't look too correct either (is there really no 
> other way to deassert CS than doing dummy read?). 
Not that I am aware of. Did you wrote that mxs_spi driver? How did you interpret the 
chips reference manual. I understood it this way: you need to tell the controller
to deassert chip select before the final transfer.

I could be possible to change the driver implementation and use GPIOs for 
chip select. But I think that's not the philisophy of this controller.

> Do you see an issue with 
> current implementation on some board please?
Yes, I installed an SST25VF032B SPI on the MX28EVK in preparation of our 
own board. The chip was detected correctly after power on, but erasing
(that's one place where the status register polling is used) more than one page
does not work and then after reset the device is not correctly detected.

I would expect problems on the M28EVK (Denx) also. You might want to turn 
SPI + spi_flash debugging to see it. Also I found a posting from
Alexander Keller on the u-boot list from 12/13/2011. Perhaps the can check if
this patch fixes his problems also.

Matthias
> 
>>
>> Signed-off-by: Matthias Fuchs <matthias.fuchs at esd.eu>
>> ---
>>  drivers/spi/mxs_spi.c |   12 +++++++++---
>>  1 files changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/spi/mxs_spi.c b/drivers/spi/mxs_spi.c
>> index 4c27fef..adb9ca8 100644
>> --- a/drivers/spi/mxs_spi.c
>> +++ b/drivers/spi/mxs_spi.c
>> @@ -129,9 +129,15 @@ int spi_xfer(struct spi_slave *slave, unsigned int
>> bitlen, int len = bitlen / 8;
>>  	const char *tx = dout;
>>  	char *rx = din;
>> -
>> -	if (bitlen == 0)
>> -		return 0;
>> +	char dummy;
>> +
>> +	if (bitlen == 0) {
>> +		if (flags & SPI_XFER_END) {
>> +			rx = &dummy;
>> +			len = 1;
>> +		} else
>> +			return 0;
>> +	}
>>
>>  	if (!rx && !tx)
>>  		return 0;
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