RE: [PATCH] devicetree/bindings: Add binding for micron n25q512a memory

[Priyanka Jain <Priyanka.Jain@xxxxxxxxxxxxx>]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, July 08, 2014 2:56 AM
> To: Jain Priyanka-B32167
> Cc: devicetree@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; linux-
> spi@xxxxxxxxxxxxxxx; linux-mtd@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH] devicetree/bindings: Add binding for micron n25q512a
> memory
> 
> On Thu, 2014-07-03 at 23:08 -0500, Jain Priyanka-B32167 wrote:
> >
> > > -----Original Message-----
> > > From: Wood Scott-B07421
> > > Sent: Friday, July 04, 2014 3:40 AM
> > > To: Jain Priyanka-B32167
> > > Cc: devicetree@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> > > linux- spi@xxxxxxxxxxxxxxx; linux-mtd@xxxxxxxxxxxxxxxxxxx
> > > Subject: Re: [PATCH] devicetree/bindings: Add binding for micron
> > > n25q512a memory
> > >
> > > On Thu, 2014-07-03 at 15:42 +0530, Priyanka Jain wrote:
> > > > -Micron n25q512a memory is supported by m25p80 driver.
> > > >  Add compatible field required to support n25q512a in m25p80.txt
> > > > -Add micron to the vendor-prefixes.txt file
> > > >
> > > > Signed-off-by: Priyanka Jain <Priyanka.Jain@xxxxxxxxxxxxx>
> > > > ---
> > > >  Documentation/devicetree/bindings/mtd/m25p80.txt   |    1 +
> > > >  .../devicetree/bindings/vendor-prefixes.txt        |    1 +
> > > >  2 files changed, 2 insertions(+), 0 deletions(-)
> > >
> > > Why did you send this to the ppc list but not the spi or mtd lists?
> > >
> > [Jain Priyanka-B32167] Sorry, I missed that
> > > I'm having a hard time following the flow of how these SPI devices
> > > get bound -- is the compatible involved at all?  I don't see this
> > > string (with vendor prefix included) in the driver.  I do see a
> > > table that contains what looks like device IDs.  If the device can
> > > report its id, shouldn't we rely on that rather than device tree
> compatible?
> > >
> > > -Scott
> > [Jain Priyanka-B32167]
> > Spi driver has a check to device name corresponding to device-id and
> compare to what is passed in dts string.
> 
> Please go into more detail.  I don't see where the string
> "micron,n25q512a" appears in the current kernel.  I do see "n25q512a",
> but how does that compare successfully with the version of the string
> that has a vendor compatible?
> 
> Again, is there a device ID that can be read at runtime?  Is there a
> compatible string that represents a common programming interface?
[Jain Priyanka-B32167] 
Spi driver (of_register_spi_devices()) search for compatible string in device-tree. It selects the flash device driver based on the compatible string (n25q512a). This compatible string is essential, else device probe wont continue.  Then Device-id of flash is read at runtime in probe and compared with the corresponding device-id of flash (n25q512a). Device-id (maintained as first element in INFO string in spi_nor_ids[] in drivers/mtd/spi-nor/spi-nor.c file)
Only if both device-ids match, the device is taken as successfully detected.
Regarding vendor "micron", you are right currently the vendor information is not maintained as such in device-id, but the convention that is followed for compatible string is "vendor-id, device-id"
> 
> > New checkpatch script search for exact string match in binding folder.
> So, I have added this in example.
> 
> That check has a lot of false positives when it comes to compatible
> strings for specific chips that don't need to be specifically mentioned
> in a more generic binding.
> 
> -Scott
> 
[Jain Priyanka-B32167] Even though "micron,n25q512a" is in sync with binding mentioned in " Documentation/devicetree/bindings/mtd/m25p80.txt   ", I have to add this as an a example, just to avoid checkpatch error. What should be the approach going forward: Should such checkpatch warnings be ignored?




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