Re: [PATCH v2] media: camss: Allocate camss struct as a managed device resource

[Robert Foss <robert.foss@linaro.org>]

On Thu, 19 May 2022 at 09:16, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>
> Robert, Vladimir,
>
> On 5/19/22 07:14, Vladimir Zapolskiy wrote:
> > The change simplifies driver's probe and remove functions, no functional
> > change is intended.
> >
> > Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
> > ---
> > Changes from v1 to v2:
> > * rebased on top of media/master
> >
> >  drivers/media/platform/qcom/camss/camss.c | 33 +++++++----------------
> >  1 file changed, 10 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> > index 79ad82e233cb..2055233af101 100644
> > --- a/drivers/media/platform/qcom/camss/camss.c
> > +++ b/drivers/media/platform/qcom/camss/camss.c
> > @@ -1529,7 +1529,7 @@ static int camss_probe(struct platform_device *pdev)
> >       struct camss *camss;
> >       int num_subdevs, ret;
> >
> > -     camss = kzalloc(sizeof(*camss), GFP_KERNEL);
> > +     camss = devm_kzalloc(dev, sizeof(*camss), GFP_KERNEL);
>
> In general it is not a good idea to use devm_*alloc. The problem is that if a
> device instance is forcibly unbound, then all the memory allocated with devm_
> is immediately freed. But if an application still has a file handle to a device
> open, then it can still use that memory.
>
> Now in this case the driver is already using devm_kcalloc, so it doesn't matter,
> but it is something to keep in mind. In general, hotpluggable devices cannot use
> devm_*alloc.
>
> In general, my recommendation is to not use devm_*alloc for this, but since it
> is already in use in this driver, it's better to use devm_*alloc consistently.
> Or, alternatively, not use it all. That's up to Robert.
>
> This is just as background information.


Thanks for explaining the nuances Hans, that's very helpful.

I think this patch is ok, since it doesn't make the situation any worse,
and that CSI camera sensors are very likely to be hotplugged.

>
> Regards,
>
>         Hans
>
> >       if (!camss)
> >               return -ENOMEM;
> >
> > @@ -1567,39 +1567,30 @@ static int camss_probe(struct platform_device *pdev)
> >               camss->csid_num = 4;
> >               camss->vfe_num = 4;
> >       } else {
> > -             ret = -EINVAL;
> > -             goto err_free;
> > +             return -EINVAL;
> >       }
> >
> >       camss->csiphy = devm_kcalloc(dev, camss->csiphy_num,
> >                                    sizeof(*camss->csiphy), GFP_KERNEL);
> > -     if (!camss->csiphy) {
> > -             ret = -ENOMEM;
> > -             goto err_free;
> > -     }
> > +     if (!camss->csiphy)
> > +             return -ENOMEM;
> >
> >       camss->csid = devm_kcalloc(dev, camss->csid_num, sizeof(*camss->csid),
> >                                  GFP_KERNEL);
> > -     if (!camss->csid) {
> > -             ret = -ENOMEM;
> > -             goto err_free;
> > -     }
> > +     if (!camss->csid)
> > +             return -ENOMEM;
> >
> >       if (camss->version == CAMSS_8x16 ||
> >           camss->version == CAMSS_8x96) {
> >               camss->ispif = devm_kcalloc(dev, 1, sizeof(*camss->ispif), GFP_KERNEL);
> > -             if (!camss->ispif) {
> > -                     ret = -ENOMEM;
> > -                     goto err_free;
> > -             }
> > +             if (!camss->ispif)
> > +                     return -ENOMEM;
> >       }
> >
> >       camss->vfe = devm_kcalloc(dev, camss->vfe_num, sizeof(*camss->vfe),
> >                                 GFP_KERNEL);
> > -     if (!camss->vfe) {
> > -             ret = -ENOMEM;
> > -             goto err_free;
> > -     }
> > +     if (!camss->vfe)
> > +             return -ENOMEM;
> >
> >       v4l2_async_nf_init(&camss->notifier);
> >
> > @@ -1681,8 +1672,6 @@ static int camss_probe(struct platform_device *pdev)
> >       v4l2_device_unregister(&camss->v4l2_dev);
> >  err_cleanup:
> >       v4l2_async_nf_cleanup(&camss->notifier);
> > -err_free:
> > -     kfree(camss);
> >
> >       return ret;
> >  }
> > @@ -1709,8 +1698,6 @@ void camss_delete(struct camss *camss)
> >               device_link_del(camss->genpd_link[i]);
> >               dev_pm_domain_detach(camss->genpd[i], true);
> >       }
> > -
> > -     kfree(camss);
> >  }
> >
> >  /*

Reviewed-by: Robert Foss <robert.foss@linaro.org>