Re: [PATCH v2] media: bcm2835-unicam: Fix log status runtime access

[Sakari Ailus]

Hi Eugen, others,

On Fri, May 29, 2026 at 06:06:42PM +0300, Eugen Hristev wrote:
> On 5/29/26 08:12, Jean-Michel Hautbois wrote:
> > Hi Eugen,
> > 
> > Le 22/05/2026 à 17:28, Eugen Hristev a écrit :
> >> When requesting log status, the block might be powered off, but registers
> >> are being read.
> >> Avoid reading the registers if the device is not resumed, thus also avoid
> >> powering up the device just for log status.
> >>
> >> Fixes: 392cd78d495f ("media: bcm2835-unicam: Add support for CCP2/CSI2 camera interface")
> >> Signed-off-by: Eugen Hristev <ehristev@xxxxxxxxxx>
> >> ---
> >> Changes in v2:
> >> - changed to use pm_runtime_get_if_active()
> >> - add corresponding put()
> >> - Link to v1: https://patch.msgid.link/20260521-bcmpipm-v1-1-3eba88d88045@xxxxxxxxxx
> >>
> >> To: Raspberry Pi Kernel Maintenance <kernel-list@xxxxxxxxxxxxxxx>
> >> To: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> >> To: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
> >> To: Ray Jui <rjui@xxxxxxxxxxxx>
> >> To: Scott Branden <sbranden@xxxxxxxxxxxx>
> >> To: Broadcom internal kernel review list <bcm-kernel-feedback-list@xxxxxxxxxxxx>
> >> To: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> >> To: Jean-Michel Hautbois <jeanmichel.hautbois@xxxxxxxxxx>
> >> To: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> >> To: Hans Verkuil <hverkuil@xxxxxxxxxx>
> >> To: Naushir Patuck <naush@xxxxxxxxxxxxxxx>
> >> Cc: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
> >> Cc: linux-media@xxxxxxxxxxxxxxx
> >> Cc: linux-rpi-kernel@xxxxxxxxxxxxxxxxxxx
> >> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> >> Cc: linux-kernel@xxxxxxxxxxxxxxx
> >> ---
> >>   drivers/media/platform/broadcom/bcm2835-unicam.c | 9 +++++++++
> >>   1 file changed, 9 insertions(+)
> >>
> >> diff --git a/drivers/media/platform/broadcom/bcm2835-unicam.c b/drivers/media/platform/broadcom/bcm2835-unicam.c
> >> index 8d28ba0b59a3..93815b8ab930 100644
> >> --- a/drivers/media/platform/broadcom/bcm2835-unicam.c
> >> +++ b/drivers/media/platform/broadcom/bcm2835-unicam.c
> >> @@ -2052,6 +2052,13 @@ static int unicam_log_status(struct file *file, void *fh)
> >>   		 node->fmt.fmt.pix.width, node->fmt.fmt.pix.height);
> >>   	dev_info(unicam->dev, "V4L2 format:         %08x\n",
> >>   		 node->fmt.fmt.pix.pixelformat);
> >> +
> >> +	if (!pm_runtime_get_if_active(unicam->dev)) {
> > 
> > Well, if I am picky I would say that pm_runtime_get_if_active() can 
> > return -EINVAL if runtime PM is disabled for the device. It should then 
> > be tested against '<= 0' ?
> > 
> > I suppose this should not happen really often, as very few drivers 
> > actually test this case...
> 
> I saw that. Some do. This driver enables runtime pm in probe though. So
> I guess it cannot happen, unless runtime pm would not selected in kernel
> config, but the driver depends on PM.

Runtime PM can be disabled for a device via sysfs.

> 
> Ultimately I guess it's up to Sakari or Hans to decide whether it's
> worth checking for error code, but I picked the simpler path (and
> considering <depends on PM> in Kconfig) .

pm_runtime_put() musn't be called if there was an error as it decrements
usage_count unconditionally.

The vast majority of sensor drivers test for non-zero only and no-one has
complained. They should be fixed though...

> > 
> > With or without this small change:
> > Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@xxxxxxxxxx>
> > 
> > Thanks,
> > JM
> > 
> >> +		dev_info(unicam->dev,
> >> +			 "Live data N/A due to device inactive\n");
> >> +		return 0;
> >> +	}
> >> +
> >>   	reg = unicam_reg_read(unicam, UNICAM_IPIPE);
> >>   	dev_info(unicam->dev, "Unpacking/packing:   %u / %u\n",
> >>   		 unicam_get_field(reg, UNICAM_PUM_MASK),
> >> @@ -2065,6 +2072,8 @@ static int unicam_log_status(struct file *file, void *fh)
> >>   	dev_info(unicam->dev, "Write pointer:       %08x\n",
> >>   		 unicam_reg_read(unicam, UNICAM_IBWP));
> >>   
> >> +	pm_runtime_put(unicam->dev);
> >> +
> >>   	return 0;
> >>   }
> >>   
> >>
> >> ---
> >> base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
> >> change-id: 20260521-bcmpipm-6c578e73239c
> >>
> >> Best regards,

-- 
Regards,

Sakari Ailus