On 5 August 2015 at 14:44, Mark Brown [off-list ref] wrote:

On Wed, Aug 05, 2015 at 02:40:01PM +0200, Michal Suchanek wrote:

quoted

On 5 August 2015 at 13:50, Mark Brown [off-list ref] wrote:

quoted

quoted

As far as I can tell you want to set a per spi_message flag saying that
the message is a flash read command?  If that's what this is trying to
do then why do you need to set the flag at all?  If the message is in a
clearly defined format and it's more efficient to use this mmap mode
then surely the driver can just recognise that the format is approprate
and switch into mmap mode without being explicitly told - I'm not clear
what the flag adds here.

quoted

ehm, the read command is just one byte.

quoted

I don't think sending 03 or other random byte as the first byte of a
SPI transfer can be used as reliable detection that we are talking to
a SPI flash memory.

Why care - if something is physically in the same format as a flash read
command how would a device be able to tell that it wasn't actually a
flash read command?  The signals sent on the bus are going to be
identical anyway.

Not only must the command be the same but also the response must be tha same.

The flash chip responds by sending arbitrary amount of data. Given
that transfer_one gets only the part that sends the read command and
the part to do the actual read may or may not follow this is getting a
bit hairy. Add in dummy bytes due to fast-read lag and page write
wrap-around and you get something that you definitely do not want
unless you are really sure that there is a flash memory on the other
end of the wire.

Thanks

Michal