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    SubjectRe: [PATCH 32/36] dmaengine: idxd: use const struct bus_type *
    On Mon, Mar 13, 2023 at 12:07:27PM -0700, Fenghua Yu wrote:
    > Hi, Greg,
    >
    > On 3/13/23 11:29, Greg Kroah-Hartman wrote:
    > > In the functions unbind_store() and bind_store(), a struct bus_type *
    > > should be a const one, as the driver core bus functions used by this
    > > variable are expecting the pointer to be constant, and these functions
    > > do not modify the pointer at all.
    > >
    > > Cc: Fenghua Yu <fenghua.yu@intel.com>
    > > Cc: Dave Jiang <dave.jiang@intel.com>
    > > Cc: Vinod Koul <vkoul@kernel.org>
    > > Cc: dmaengine@vger.kernel.org
    > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > > ---
    > > Note, this is a patch that is a prepatory cleanup as part of a larger
    > > series of patches that is working on resolving some old driver core
    > > design mistakes. It will build and apply cleanly on top of 6.3-rc2 on
    > > its own, but I'd prefer if I could take it through my driver-core tree
    > > so that the driver core changes can be taken through there for 6.4-rc1.
    > >
    > > drivers/dma/idxd/compat.c | 4 ++--
    > > 1 file changed, 2 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/drivers/dma/idxd/compat.c b/drivers/dma/idxd/compat.c
    > > index 3df21615f888..5fd38d1b9d28 100644
    > > --- a/drivers/dma/idxd/compat.c
    > > +++ b/drivers/dma/idxd/compat.c
    > > @@ -16,7 +16,7 @@ extern void device_driver_detach(struct device *dev);
    > > static ssize_t unbind_store(struct device_driver *drv, const char *buf, size_t count)
    > > {
    > > - struct bus_type *bus = drv->bus;
    > > + const struct bus_type *bus = drv->bus;
    > > struct device *dev;
    > > int rc = -ENODEV;
    > > @@ -32,7 +32,7 @@ static DRIVER_ATTR_IGNORE_LOCKDEP(unbind, 0200, NULL, unbind_store);
    > > static ssize_t bind_store(struct device_driver *drv, const char *buf, size_t count)
    > > {
    > > - struct bus_type *bus = drv->bus;
    > > + const struct bus_type *bus = drv->bus;
    > > struct device *dev;
    > > struct device_driver *alt_drv = NULL;
    > > int rc = -ENODEV;
    >
    > After applying this patch, warning is reported:
    >
    > drivers/dma/idxd/compat.c: In function ‘bind_store’:
    > drivers/dma/idxd/compat.c:47:47: warning: passing argument 2 of
    > ‘driver_find’ discards ‘const’ qualifier from pointer target type
    > [-Wdiscarded-qualifiers]
    > 47 | alt_drv = driver_find("idxd", bus);
    > | ^~~
    > In file included from ./include/linux/device.h:32,
    > from drivers/dma/idxd/compat.c:6:
    > ./include/linux/device/driver.h:129:59: note: expected ‘struct bus_type *’
    > but argument is of type ‘const struct bus_type *’
    > 129 | struct bus_type *bus);
    > | ~~~~~~~~~~~~~~~~~^~~
    >
    > Should the "bus" parameter in driver_find() definition be changed to const
    > as well to avoid the warning?

    Oops, yes, it needs an earlier patch in this series, sorry, I didn't
    call that out properly in the notes section of the patch.

    So I can just take this through my tree if that's ok.

    thanks,

    greg k-h

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