iommu/tegra-smmu: fix error checking for debugfs_create_dir()

The return value of debugfs_create_dir() should be checked using the
IS_ERR() function.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
---

 drivers/iommu/tegra-smmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On 2023/10/25 19:01, Dario Binacchi wrote:
> The return value of debugfs_create_dir() should be checked using the
> IS_ERR() function.
> 
> Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> ---
> 
>   drivers/iommu/tegra-smmu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> index e445f80d0226..cd1d80c4c673 100644
> --- a/drivers/iommu/tegra-smmu.c
> +++ b/drivers/iommu/tegra-smmu.c
> @@ -1056,7 +1056,7 @@ DEFINE_SHOW_ATTRIBUTE(tegra_smmu_clients);
>   static void tegra_smmu_debugfs_init(struct tegra_smmu *smmu)
>   {
>   	smmu->debugfs = debugfs_create_dir("smmu", NULL);
> -	if (!smmu->debugfs)
> +	if (IS_ERR(smmu->debugfs))
>   		return;

This check can be removed, as debugfs_create_file() can handle the case
where @parent is an error pointer.

>   
>   	debugfs_create_file("swgroups", S_IRUGO, smmu->debugfs, smmu,

Best regards,
baolu

On Wed, Oct 25, 2023 at 07:25:50PM +0800, Baolu Lu wrote:
> On 2023/10/25 19:01, Dario Binacchi wrote:
> > The return value of debugfs_create_dir() should be checked using the
> > IS_ERR() function.
> > 
> > Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> > ---
> > 
> >   drivers/iommu/tegra-smmu.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> > index e445f80d0226..cd1d80c4c673 100644
> > --- a/drivers/iommu/tegra-smmu.c
> > +++ b/drivers/iommu/tegra-smmu.c
> > @@ -1056,7 +1056,7 @@ DEFINE_SHOW_ATTRIBUTE(tegra_smmu_clients);
> >   static void tegra_smmu_debugfs_init(struct tegra_smmu *smmu)
> >   {
> >   	smmu->debugfs = debugfs_create_dir("smmu", NULL);
> > -	if (!smmu->debugfs)
> > +	if (IS_ERR(smmu->debugfs))
> >   		return;
> 
> This check can be removed, as debugfs_create_file() can handle the case
> where @parent is an error pointer.

A patch for this has been in linux-next for a few weeks, see:

commit f7da9c081517daba70f9f9342e09d7a6322ba323
Author: Jinjie Ruan <ruanjinjie@huawei.com>
Date:   Fri Sep 1 15:30:56 2023 +0800

    iommu/tegra-smmu: Drop unnecessary error check for for debugfs_create_dir()
    
    The debugfs_create_dir() function returns error pointers.
    It never returns NULL.
    
    As Baolu suggested, this patch removes the error checking for
    debugfs_create_dir in tegra-smmu.c. This is because the DebugFS kernel API
    is developed in a way that the caller can safely ignore the errors that
    occur during the creation of DebugFS nodes. The debugfs APIs have
    a IS_ERR() judge in start_creating() which can handle it gracefully. So
    these checks are unnecessary.
    
    Fixes: d1313e7896e9 ("iommu/tegra-smmu: Add debugfs support")
    Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
    Suggested-by: Baolu Lu <baolu.lu@linux.intel.com>
    Acked-by: Thierry Reding <treding@nvidia.com>
    Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
    Link: https://lore.kernel.org/r/20230901073056.1364755-1-ruanjinjie@huawei.com
    Signed-off-by: Joerg Roedel <jroedel@suse.de>

Thierry

Hello Thierry,

On Mon, Oct 30, 2023 at 4:30 PM Thierry Reding <thierry.reding@gmail.com> wrote:
>
> On Wed, Oct 25, 2023 at 07:25:50PM +0800, Baolu Lu wrote:
> > On 2023/10/25 19:01, Dario Binacchi wrote:
> > > The return value of debugfs_create_dir() should be checked using the
> > > IS_ERR() function.
> > >
> > > Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> > > ---
> > >
> > >   drivers/iommu/tegra-smmu.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> > > index e445f80d0226..cd1d80c4c673 100644
> > > --- a/drivers/iommu/tegra-smmu.c
> > > +++ b/drivers/iommu/tegra-smmu.c
> > > @@ -1056,7 +1056,7 @@ DEFINE_SHOW_ATTRIBUTE(tegra_smmu_clients);
> > >   static void tegra_smmu_debugfs_init(struct tegra_smmu *smmu)
> > >   {
> > >     smmu->debugfs = debugfs_create_dir("smmu", NULL);
> > > -   if (!smmu->debugfs)
> > > +   if (IS_ERR(smmu->debugfs))
> > >             return;
> >
> > This check can be removed, as debugfs_create_file() can handle the case
> > where @parent is an error pointer.
>
> A patch for this has been in linux-next for a few weeks, see:
>
> commit f7da9c081517daba70f9f9342e09d7a6322ba323
> Author: Jinjie Ruan <ruanjinjie@huawei.com>
> Date:   Fri Sep 1 15:30:56 2023 +0800
>
>     iommu/tegra-smmu: Drop unnecessary error check for for debugfs_create_dir()
>
>     The debugfs_create_dir() function returns error pointers.
>     It never returns NULL.
>
>     As Baolu suggested, this patch removes the error checking for
>     debugfs_create_dir in tegra-smmu.c. This is because the DebugFS kernel API
>     is developed in a way that the caller can safely ignore the errors that
>     occur during the creation of DebugFS nodes. The debugfs APIs have
>     a IS_ERR() judge in start_creating() which can handle it gracefully. So
>     these checks are unnecessary.
>
>     Fixes: d1313e7896e9 ("iommu/tegra-smmu: Add debugfs support")
>     Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
>     Suggested-by: Baolu Lu <baolu.lu@linux.intel.com>
>     Acked-by: Thierry Reding <treding@nvidia.com>
>     Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
>     Link: https://lore.kernel.org/r/20230901073056.1364755-1-ruanjinjie@huawei.com
>     Signed-off-by: Joerg Roedel <jroedel@suse.de>
>

Thanks for the explanation,
regards
Dario

> Thierry