[RFC PATCH 1/5] spi: introduce flag for memory mapped read

Mark Brown broonie at kernel.org
Wed Aug 5 05:44:12 PDT 2015

On Wed, Aug 05, 2015 at 02:40:01PM +0200, Michal Suchanek wrote:
> On 5 August 2015 at 13:50, Mark Brown <broonie at kernel.org> wrote:

> > 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.

> ehm, the read command is just one byte.

> 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.
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