Re: [PATCH v7 0/4] Extend device_get_match_data() to struct bus_type

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 5 Aug 2023 17:42:21 +0000
Biju Das <biju.das.jz@bp.renesas.com> wrote:

> Hi Jonathan Cameron,
> 
> Thanks for the feedback.
> 
> > Subject: Re: [PATCH v7 0/4] Extend device_get_match_data() to struct
> > bus_type
> > 
> > On Fri,  4 Aug 2023 17:17:24 +0100
> > Biju Das <biju.das.jz@bp.renesas.com> wrote:
> >   
> > > This patch series extend device_get_match_data() to struct bus_type,
> > > so that buses like I2C can get matched data.
> > >
> > > There is a plan to replace
> > > i2c_get_match_data()->device_get_match_data()
> > > later, once this patch hits mainline as it is redundant.  
> > 
> > Are we sure we don't have any instances left of the pattern that used to
> > be common (typically for drivers where dt tables were added
> > later) of
> > 
> > 	chip_info = device_get_match_data();
> > 	if (!chip_info) {
> > 		chip_info = arrayofchipinfo[id->driver_data];
> > 	}
> > 
> > Looks like the first driver I checked, iio/adc/max1363.c does this still
> > and will I think break with this series.
> > 
> > Or am I missing some reason this isn't a problem?  
> 
> Good catch, this will break.
> we need to make I2C table like OF/ACPI tables.
> 
> Yes, before adding callback support to i2c_device_get_match_data(),
> We need to make similar table for OF/ACPI/I2C for all i2c drivers
> that use device_get_match_data()or of_get_device_match_data().

To throw another option out there, could we make the I2C subsystem use
the of_device_id table in place of the i2c_device_id table? 
That is perform matches based only on the of_device_id table in all
drivers (with some glue code making that work for the less common paths,
remaining board files etc). The ACPI PRP0001 magic is doing similar
already.

I can't immediately see why that wouldn't work other than being a bit
of a large job to implement in all drivers.

Getting rid of the duplication would be good.  Probably some rough corners
to make it possible to do this in a gradual process. In particular some
of the naming used for i2c_device_id table entries won't be 'valid'
DT compatibles (minus the vendor id)

> 
> May be first intermediate step is to use i2c_get_match_data()
> For such table conversion. Once all table conversion is done
> then we can add i2c_device_get_match_data() callback.
> 
> The below one is the recommendation from Andy.
> 
> + * Besides the fact that some drivers abuse the device ID driver_data type
> + * and claim it to be integer, for the bus specific ID tables the driver_data
> + * may be defined as kernel_ulong_t. For these tables 0 is a valid response,
> + * but not for this function. It's recommended to convert those either to avoid
> + * 0 or use a real pointer to the predefined driver data.
> + */

We still need to maintain consistency across the two tables, which
is a stronger requirement than avoiding 0.  Some drivers already do that by
forcing the enum used to start at 1 which doesn't solver the different data
types issue.

Jonathan

> 
> > 
> > Clearly this only matters if we get to the bus callback, but enabling that
> > is the whole point of this series.  Hence I think a lot of auditing is
> > needed before this can be safely applied.  
> 
> Sure.
> 
> Cheers,
> Biju
> 
> > 
> > Jonathan
> >   
> > > v6->v7:
> > >  * Added ack from Greg Kroah-Hartman for patch#1
> > >  * Swapped patch#2 and patch#3 from v6.
> > >  * Added Rb tag from Andy for patch#2 and patch#4
> > >  * Updated commit description of patch#2 by removing unnecessary  
> > wrapping.  
> > >  * Updated typo in commit description struct bus_type()->struct  
> > bus_type.  
> > > v5->v6:
> > >  * Cced linux-rtc and linux-iio as these subsytems uses i2c_get_match_
> > >    data() and this function become redundant once this patch series hits
> > >    mainline.
> > >  * Added Rb tag from Sakari for patch#1.
> > >  * Moved patch#3 from v5 to patch#2 and patch#2 from v5 to patch#4.
> > >  * Added Rb tag from Andy for patch#2
> > >  * Separate patch#3 to prepare for better difference for
> > >    i2c_match_id() changes.
> > >  * Merged patch#4 from v5 with patch#4.
> > > v4->v5:
> > >  * Added const struct device_driver variable 'drv' in  
> > i2c_device_get_match  
> > >    _data().
> > >  * For code readability and maintenance perspective, added separate NULL
> > >    check for drv and client variable and added comment for NULL check  
> > for  
> > >    drv variable.
> > >  * Created separate patch for converting i2c_of_match_device_sysfs() to
> > >    non-static.
> > >  * Removed export symbol for i2c_of_match_device_sysfs().
> > >  * Replaced 'dev->driver'->'drv'.
> > >  * Replaced return value data->NULL to avoid (potentially) stale  
> > pointers,  
> > >    if there is no match.
> > > v3->v4:
> > >  * Documented corner case for device_get_match_data()
> > >  * Dropped struct i2c_driver parameter from
> > > i2c_get_match_data_helper()
> > >  * Split I2C sysfs handling in separate patch(patch#3)
> > >  * Added space after of_device_id for i2c_of_match_device_sysfs()
> > >  * Added const parameter for struct i2c_client, to prevent overriding  
> > it's  
> > >    pointer.
> > >  * Moved declaration from public i2c.h->i2c-core.h
> > > v2->v3:
> > >  * Added Rb tag from Andy for patch#1.
> > >  * Extended to support i2c_of_match_device() as suggested by Andy.
> > >  * Changed i2c_of_match_device_sysfs() as non-static function as it is
> > >    needed for i2c_device_get_match_data().
> > >  * Added a TODO comment to use i2c_verify_client() when it accepts const
> > >    pointer.
> > >  * Added multiple returns to make code path for device_get_match_data()
> > >    faster in i2c_get_match_data().
> > > RFC v1->v2:
> > >  * Replaced "Signed-off-by"->"Suggested-by" tag for Dmitry.
> > >  * Documented device_get_match_data().
> > >  * Added multiple returns to make code path for generic fwnode-based
> > >    lookup faster.
> > >  * Fixed build warnings reported by kernel test robot <lkp@intel.com>
> > >  * Added const qualifier to return type and parameter struct i2c_driver
> > >    in i2c_get_match_data_helper().
> > >  * Added const qualifier to struct i2c_driver in i2c_get_match_data()
> > >  * Dropped driver variable from i2c_device_get_match_data()
> > >  * Replaced to_i2c_client with logic for assigning verify_client as it
> > >    returns non const pointer.
> > >
> > > Biju Das (4):
> > >   drivers: fwnode: Extend device_get_match_data() to struct bus_type
> > >   i2c: Enhance i2c_get_match_data()
> > >   i2c: i2c-core-of: Convert i2c_of_match_device_sysfs() to non-static
> > >   i2c: Add i2c_device_get_match_data() callback
> > >
> > >  drivers/base/property.c     | 27 ++++++++++++++++-
> > >  drivers/i2c/i2c-core-base.c | 60 ++++++++++++++++++++++++++++++-------
> > >  drivers/i2c/i2c-core-of.c   |  4 +--
> > >  drivers/i2c/i2c-core.h      |  9 ++++++
> > >  include/linux/device/bus.h  |  3 ++
> > >  5 files changed, 90 insertions(+), 13 deletions(-)
> > >  
>