On Saturday 22 June 2024 16:29:21 Hans de Goede wrote: > Hi, > > On 6/22/24 4:23 PM, Pali Rohár wrote: > > 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@xxxxxxxxxx> > >>>>>> --- > >>>>>> 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. > > We would still need to be very very sure the device we are calling that > function on actually has the i2c-i801.c driver bound to it, so that > e.g. we are not dereferencing a NULL pointer drvdata, or worse > poking at some other drivers private data because we are calling > the helper on the wrong device. > > To make sure that is the case we would need to e.g. check that: > a) The device in question is an i2c adapter > b) the adapter name matches, so we would still be doing name matching ... > > Really just matching on the adapter name is by far the cleanest > option here. > > Regards, > > Hans Ok, I have looked at it now. For a) you are already using i2c_verify_adapter(). So this part is done. For b) you do not need to check adapter name, but rather adapter driver name (in case driver data are begin accessed). And I think you can use dev->driver.name to get it. Anyway, I see that pattern "to_<something>_driver" is commonly used.
