Re: [PATCH v3 2/6] i2c: i801: Use a different adapter-name for IDF adapters

["Pali Rohár" <pali@kernel.org>]

On Saturday 22 June 2024 16:14:11 Hans de Goede wrote:
> Hi Pali,
> 
> On 6/22/24 4:08 PM, Pali Rohár wrote:
> > On Saturday 22 June 2024 15:56:03 Hans de Goede wrote:
> >> Hi,
> >>
> >> On 6/22/24 2:46 PM, Pali Rohár wrote:
> >>> On Friday 21 June 2024 14:24:57 Hans de Goede wrote:
> >>>> On chipsets with a second 'Integrated Device Function' SMBus controller use
> >>>> a different adapter-name for the second IDF adapter.
> >>>>
> >>>> This allows platform glue code which is looking for the primary i801
> >>>> adapter to manually instantiate i2c_clients on to differentiate
> >>>> between the 2.
> >>>>
> >>>> This allows such code to find the primary i801 adapter by name, without
> >>>> needing to duplicate the PCI-ids to feature-flags mapping from i2c-i801.c.
> >>>>
> >>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> >>>> ---
> >>>>  drivers/i2c/busses/i2c-i801.c | 9 +++++++--
> >>>>  1 file changed, 7 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
> >>>> index d2d2a6dbe29f..5ac5bbd60d45 100644
> >>>> --- a/drivers/i2c/busses/i2c-i801.c
> >>>> +++ b/drivers/i2c/busses/i2c-i801.c
> >>>> @@ -1760,8 +1760,13 @@ static int i801_probe(struct pci_dev *dev, const struct pci_device_id *id)
> >>>>  
> >>>>  	i801_add_tco(priv);
> >>>>  
> >>>> -	snprintf(priv->adapter.name, sizeof(priv->adapter.name),
> >>>> -		"SMBus I801 adapter at %04lx", priv->smba);
> >>>> +	if (priv->features & FEATURE_IDF)
> >>>> +		snprintf(priv->adapter.name, sizeof(priv->adapter.name),
> >>>> +			"SMBus I801 IDF adapter at %04lx", priv->smba);
> >>>> +	else
> >>>> +		snprintf(priv->adapter.name, sizeof(priv->adapter.name),
> >>>> +			"SMBus I801 adapter at %04lx", priv->smba);
> >>>> +
> >>>
> >>> User visible name is identifier for user / human.
> >>>
> >>> If somebody is going to read this code in next 10 years then can ask
> >>> question why to have different name for IDF FEATURE and not also for
> >>> other features? And can come to conclusion to unify all names to be
> >>> same (why not? it is user identifier).
> >>
> >> That is a good point, I'll add a comment about this for the next
> >> version.
> >>
> >>> Depending on user names between different kernel subsystem is fragile,
> >>> specially for future as rename can happen.
> >>
> >> Relying no devices names to find devices is standard practice. E.g.
> >> this is how 99% of the platform drivers bind to platform devices
> >> by the driver and the device having the same name.
> > 
> > But here it is adapter name which is more likely description, not the
> > device name which is used for binding.
> 
> It is still matching on a name.
> 
> >>> If you are depending on FEATURE_IDF flag then check for the flag
> >>> directly, and not hiding the flag by serializing it into the user
> >>> visible name (char[] variable) and then de-serializing it in different
> >>> kernel subsystem. If the flag is not exported yet then export it via
> >>> some function or other API.
> >>
> >> Exporting this through some new function is non trivial and adds
> >> extra dependencies between modules, causing issues when one is builtin
> >> and the other is build as a module.
> > 
> > Access to "struct i801_priv *" is not possible? For example via
> > dev_get_drvdata() on "struct device *" which you have in
> > smo8800_find_i801()?
> > 
> > Because if it is possible then you can create an inline function in some
> > shared header file which access this flag. Not perfect (as accessing
> > private data is not the best thing) but can avoid dependences between
> > modules.
> 
> Prodding inside another drivers private driver struct is a big nono
> and much much more fragile then the name checking.

I know, that is why I wrote to access this structure and flags in
separate function which can be an inline in e.g. i2c-i801.h header file.

> Regards,
> 
> Hans
> 
>