[U-Boot] [PATCH V3 2/2] pci: Update documentation to make 'compatible' string optional

[Marek Vasut]

On 09/14/2018 06:41 AM, Simon Glass wrote:
> Hi Marex,

It's Marek btw ...

> On 11 September 2018 at 14:58, Marek Vasut <marek.vasut at gmail.com> wrote:
>> Reword the documentation to make it clear the compatible string is now
>> optional, yet still matching on it takes precedence over PCI IDs and
>> PCI classes.
>>
>> Signed-off-by: Marek Vasut <marek.vasut+renesas at gmail.com>
>> Cc: Simon Glass <sjg at chromium.org>
>> Cc: Tom Rini <trini at konsulko.com>
>> ---
>> V3: No change
>> V2: New patch
>> ---
>>  doc/driver-model/pci-info.txt | 14 +++++++++-----
>>  1 file changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/doc/driver-model/pci-info.txt b/doc/driver-model/pci-info.txt
>> index e1701d1fbc..14364c5c75 100644
>> --- a/doc/driver-model/pci-info.txt
>> +++ b/doc/driver-model/pci-info.txt
>> @@ -34,11 +34,15 @@ under that bus.
>>  Note that this is all done on a lazy basis, as needed, so until something is
>>  touched on PCI (eg: a call to pci_find_devices()) it will not be probed.
>>
>> -PCI devices can appear in the flattened device tree. If they do this serves to
>> -specify the driver to use for the device. In this case they will be bound at
>> -first. Each PCI device node must have a compatible string list as well as a
>> -<reg> property, as defined by the IEEE Std 1275-1994 PCI bus binding document
>> -v2.1. Note we must describe PCI devices with the same bus hierarchy as the
>> +PCI devices can appear in the flattened device tree. If they do, their node
>> +often contains extra information which cannot be derived from the PCI IDs or
>> +PCI class of the device. Each PCI device node must have a <reg> property, as
>> +defined by the IEEE Std 1275-1994 PCI bus binding document v2.1. Compatible
>> +string list is optional and generally not needed, since PCI is discoverable
> 
> I really don't like 'generally not needed'. How about 'generally not
> essential'? Or that you can usually avoid it if desired.

Must be a language nuance, but the compatible string is really not
needed. I am starting to understand where this mindset of "compat
strings are generally needed" comes from, which is the design of the
virtual PCI devices in sandbox, but that's not the usual case.

> I'd like to say that it is optional since U_BOOT_PCI_DEVICE() can be
> used to specific the driver based on conditions like the PCI vendor/,
> PCI class, etc. If U-Boot does not find a compatible string then it
> will search these U_BOOT_PCI_DEVICE() records to find a driver;
> assuming it finds one it will then search for the device-tree node
> whose reg property matches the bus/device/function of the device, and
> attached that node to the device so that it is accessible to the
> driver.

Can you rephrase it better then ? I can paste it into the docs.

>> +bus, albeit there are justified exceptions. If the compatible string is
>> +present, matching on it takes precedence over PCI IDs and PCI classes.
>> +
>> +Note we must describe PCI devices with the same bus hierarchy as the
>>  hardware, otherwise driver model cannot detect the correct parent/children
>>  relationship during PCI bus enumeration thus PCI devices won't be bound to
>>  their drivers accordingly. A working example like below:
>> --
>> 2.18.0
>>
> 
> Regards,
> Simon
> 


-- 
Best regards,
Marek Vasut