[PATCH] of: i2c: improve last resort compatible entry selection

[Grant Likely]

On Sun, Jul 27, 2008 at 1:05 AM, Jon Smirl <jonsmirl at gmail.com> wrote:
> On 7/26/08, Grant Likely <grant.likely at secretlab.ca> wrote:
>> On Mon, Jul 14, 2008 at 09:54:37PM +0400, Anton Vorontsov wrote:
>>  > Currently of_i2c will select first compatible property as a last resort
>>  > option. This isn't best choice though, because generic compatible entries
>>  > are listed last, not first. For example, two compatible entries given for
>>  > the MCU node:
>>  >
>>  > "fsl,mc9s08qg8-mpc837xrdb", "fsl,mcu-mpc8349emitx";
>>  >
>>  > Since no sane driver will ever match specific devices, what we want is
>>  > to select most generic option (last). Then driver may call
>>  > of_device_is_compatible() if it is really interested in details.
>>
>>
>> I highly suspect that this will actually be a rare condition and that
>>  most of the time the driver you want will bind against the first entry
>>  in the list (I'm basing this on what discussion I've seen on the list
>>  and it seems to me that Jiri does want i2c devices to list the exact set
>>  of chips that each driver binds against).
>
> Can we put a loop on request_module() and have it try each one down
> the list until something matches? request_module() returns errors, but
> I can't tell from the source if one of those errors is "no matching
> module found" since it invokes a user space helper.

What will request_module() do if the modules is compiled in
statically?  If it is workable then I'm not opposed to this approach.

> That would work for this compatible string:
> compatible = "atmel,24c32wp", "24c32", "eeprom";
>
> request_module will always fail for the first entry. If you have at24
> in your system the second one will succeed. If you have eeprom the
> third one works. All of those names are valid in a device tree.

I know this is just an example; but to keep thinks clear, the second
and third values in this compatible property are completely bogus (for
device trees).  The manufacturer prefix needs to be present and
'eeprom' is far to vague.

g.


-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.