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SubjectRe: [PATCH 32/36] dmaengine: idxd: use const struct bus_type *
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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?

Thanks.

-Fenghua

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