Date:   Fri, 6 Aug 2021 08:46:23 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
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        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2 0/6] PCI: Drop duplicated tracking of a pci_dev's
 bound driver

Hello Bjorn,

On Thu, Aug 05, 2021 at 06:42:34PM -0500, Bjorn Helgaas wrote:
> On Tue, Aug 03, 2021 at 12:01:44PM +0200, Uwe Kleine-König wrote:
> > Hello,
> > 
> > changes since v1 (https://lore.kernel.org/linux-pci/20210729203740.1377045-1-u.kleine-koenig@pengutronix.de):
> > 
> > - New patch to simplify drivers/pci/xen-pcifront.c, spotted and
> >   suggested by Boris Ostrovsky
> > - Fix a possible NULL pointer dereference I introduced in xen-pcifront.c
> > - A few whitespace improvements
> > - Add a commit log to patch #6 (formerly #5)
> > 
> > I also expanded the audience for patches #4 and #6 to allow affected
> > people to actually see the changes to their drivers.
> > 
> > Interdiff can be found below.
> > 
> > The idea is still the same: After a few cleanups (#1 - #3) a new macro
> > is introduced abstracting access to struct pci_dev->driver. All users
> > are then converted to use this and in the last patch the macro is
> > changed to make use of struct pci_dev::dev->driver to get rid of the
> > duplicated tracking.
> 
> I love the idea of this series!

\o/

> I looked at all the bus_type.probe() methods, it looks like pci_dev is
> not the only offender here.  At least the following also have a driver
> pointer in the device struct:
> 
>   parisc_device.driver
>   acpi_device.driver
>   dio_dev.driver
>   hid_device.driver
>   pci_dev.driver
>   pnp_dev.driver
>   rio_dev.driver
>   zorro_dev.driver

Right, when I converted zorro_dev it was pointed out that the code was
copied from pci and the latter has the same construct. :-)
See
https://lore.kernel.org/r/20210730191035.1455248-5-u.kleine-koenig@pengutronix.de
for the patch, I don't find where pci was pointed out, maybe it was on
irc only.

> Do you plan to do the same for all of them, or is there some reason
> why they need the pointer and PCI doesn't?

There is a list of cleanup stuff I intend to work on. Considering how
working on that list only made it longer in the recent past, maybe it
makes more sense to not work on it :-)

> In almost all cases, other buses define a "to_<bus>_driver()"
> interface.  In fact, PCI already has a to_pci_driver().
> 
> This series adds pci_driver_of_dev(), which basically just means we
> can do this:
> 
>   pdrv = pci_driver_of_dev(pdev);
> 
> instead of this:
> 
>   pdrv = to_pci_driver(pdev->dev.driver);
> 
> I don't see any other "<bus>_driver_of_dev()" interfaces, so I assume
> other buses just live with the latter style?  I'd rather not be
> different and have two ways to get the "struct pci_driver *" unless
> there's a good reason.

Among few the busses I already fixed in this regard pci was the first
that has a considerable amount of usage. So I considered it worth giving
it a name.
 
> Looking through the places that care about pci_dev.driver (the ones
> updated by patch 5/6), many of them are ... a little dubious to begin
> with.  A few need the "struct pci_error_handlers *err_handler"
> pointer, so that's probably legitimate.  But many just need a name,
> and should probably be using dev_driver_string() instead.

Yeah, I considered adding a function to get the driver name from a
pci_dev and a function to get the error handlers. Maybe it's an idea to
introduce these two and then use to_pci_driver(pdev->dev.driver) for the
few remaining users? Maybe doing that on top of my current series makes
sense to have a clean switch from pdev->driver to pdev->dev.driver?!

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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