linux-kernel - Re: [PATCH 32/36] dmaengine: idxd: use const struct bus

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Message-ID: <ZB1l9mWTNPrUX4FJ@kroah.com>
Date:   Fri, 24 Mar 2023 09:57:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     linux-kernel@...r.kernel.org, rafael@...nel.org,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org
Subject: Re: [PATCH 32/36] dmaengine: idxd: use const struct bus_type *

On Thu, Mar 16, 2023 at 04:57:54PM -0700, Fenghua Yu wrote:
> Hi, Greg,
> 
> On 3/16/23 03:16, Greg Kroah-Hartman wrote:
> > 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@...el.com>
> > > > Cc: Dave Jiang <dave.jiang@...el.com>
> > > > Cc: Vinod Koul <vkoul@...nel.org>
> > > > Cc: dmaengine@...r.kernel.org
> > > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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.
> 
> Sure.
> 
> Acked-by: Fenghua Yu <fenghua.yu@...el.com>

Great, thanks for this, I've now queued up the series in my tree.

greg k-h