On Thu, 2020-12-03 at 09:05 +0100, Bartosz Golaszewski wrote:
> On Mon, Nov 23, 2020 at 7:38 PM Nicolas Saenz Julienne
> <nsaenzjulienne@suse.de> wrote:
> > 
> > When unbinding the firmware device we need to make sure it has no
> > consumers left. Otherwise we'd leave them with a firmware handle
> > pointing at freed memory.
> > 
> > Keep a reference count of all consumers and introduce rpi_firmware_put()
> > which will permit automatically decrease the reference count upon
> > unbinding consumer drivers.
> > 
> > Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> > ---
> > 
> > Changes since v3:
> > - Use kref instead of waiting on refcount
> > 
> >  drivers/firmware/raspberrypi.c             | 37 +++++++++++++++++++---
> >  include/soc/bcm2835/raspberrypi-firmware.h |  2 ++
> >  2 files changed, 35 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/firmware/raspberrypi.c b/drivers/firmware/raspberrypi.c
> > index 30259dc9b805..ed793aef7851 100644
> > --- a/drivers/firmware/raspberrypi.c
> > +++ b/drivers/firmware/raspberrypi.c
> > @@ -7,6 +7,7 @@
> >   */
> > 
> >  #include <linux/dma-mapping.h>
> > +#include <linux/kref.h>
> >  #include <linux/mailbox_client.h>
> >  #include <linux/module.h>
> >  #include <linux/of_platform.h>
> > @@ -27,6 +28,8 @@ struct rpi_firmware {
> >         struct mbox_chan *chan; /* The property channel. */
> >         struct completion c;
> >         u32 enabled;
> > +
> > +       struct kref consumers;
> >  };
> > 
> >  static DEFINE_MUTEX(transaction_lock);
> > @@ -225,12 +228,27 @@ static void rpi_register_clk_driver(struct device *dev)
> >                                                 -1, NULL, 0);
> >  }
> > 
> > +static void rpi_firmware_delete(struct kref *kref)
> > +{
> > +       struct rpi_firmware *fw = container_of(kref, struct rpi_firmware,
> > +                                              consumers);
> > +
> > +       mbox_free_channel(fw->chan);
> > +       kfree(fw);
> > +}
> > +
> > +void rpi_firmware_put(struct rpi_firmware *fw)
> > +{
> > +       kref_put(&fw->consumers, rpi_firmware_delete);
> > +}
> > +EXPORT_SYMBOL_GPL(rpi_firmware_put);
> > +
> >  static int rpi_firmware_probe(struct platform_device *pdev)
> >  {
> >         struct device *dev = &pdev->dev;
> >         struct rpi_firmware *fw;
> > 
> > -       fw = devm_kzalloc(dev, sizeof(*fw), GFP_KERNEL);
> 
> One nit from my side: maybe add a comment here saying that you really
> want to use non-managed kzalloc() because you're going to get people
> blindly converting it to devm_kzalloc() very soon.

Good point, I'll change it.

Regards,
Nicolas