[U-Boot] [PATCH v2 08/10] dm: syscon: Provide a generic syscon driver

[Paul Burton]

On 01/08/16 03:20, Simon Glass wrote:
> Hi Paul,
>
> On 27 July 2016 at 08:26, Paul Burton <paul.burton at imgtec.com> wrote:
>> Provide a trivial syscon driver matching the generic "syscon" compatible
>> string, allowing for simple system controllers to be used without a
>> custom driver just as in Linux.
>>
>> Signed-off-by: Paul Burton <paul.burton at imgtec.com>
>>
>> ---
>>
>> Changes in v2:
>> - New patch
>>
>>  drivers/core/syscon-uclass.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/core/syscon-uclass.c b/drivers/core/syscon-uclass.c
>> index 01bd968..2148469 100644
>> --- a/drivers/core/syscon-uclass.c
>> +++ b/drivers/core/syscon-uclass.c
>> @@ -95,3 +95,14 @@ UCLASS_DRIVER(syscon) = {
>>         .per_device_auto_alloc_size = sizeof(struct syscon_uc_info),
>>         .pre_probe = syscon_pre_probe,
>>  };
>> +
>> +static const struct udevice_id generic_syscon_ids[] = {
>> +       { .compatible = "syscon" },
>> +       { }
>> +};
>> +
>> +U_BOOT_DRIVER(generic_syscon) = {
>> +       .name   = "syscon",
>> +       .id     = UCLASS_SYSCON,
>> +       .of_match = generic_syscon_ids,
>> +};
>> --
>> 2.9.0
>>
>
> This would work if driver model checked compatible strings in priority
> order. But it does not.
>
> lists_bind_fdt() checks every driver to see if it is compatible. So
> your driver may be picked in preference to a more specific one.
>
> I've been aware of this limitation but it hasn't come up until now.
>
> I suppose the solution is to flip things around so that we:
>
> 1. Pick a node
> 2. Look at each compatible string in turn, starting from the first
> (most specific)
> 3. Search for a driver for that string
>
> Do you want to take a look?
>
> Regards,
> Simon
>

Hi Simon,

Ah - I wasn't aware of that discrepancy vs the device tree spec. I've 
just submitted v4 of my series which introduces a new patch 8 "dm: core: 
Match compatible strings in order of priority" which should fix that.

Thanks,
     Paul