linux-kernel - Re: [PATCH] memory: tegra20-emc: replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS

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Date:   Tue, 1 Nov 2022 13:12:20 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Bo Liu <liubo03@...pur.com>
Cc:     krzysztof.kozlowski@...aro.org, jonathanh@...dia.com,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH] memory: tegra20-emc: replace DEFINE_SIMPLE_ATTRIBUTE
 with DEFINE_DEBUGFS_ATTRIBUTE

On Tue, Nov 01, 2022 at 12:52:14PM +0100, Thierry Reding wrote:
> On Tue, Nov 01, 2022 at 04:16:11AM -0400, Bo Liu wrote:
> > Fix the following coccicheck warning:
> >  drivers/memory/tegra/tegra20-emc.c:902:0-23: WARNING:
> >   tegra_emc_debug_max_rate_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE
> >  drivers/memory/tegra/tegra20-emc.c:872:0-23: WARNING:
> >   tegra_emc_debug_min_rate_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE
> > 
> > Signed-off-by: Bo Liu <liubo03@...pur.com>
> > ---
> >  drivers/memory/tegra/tegra20-emc.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> This seems incomplete: the rationale in that debugfs cocci script says
> that DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe() is the
> pattern to use vs. the less efficient DEFINE_SIMPLE_ATTRIBUTE +
> debugfs_create_file(). So this patch should probably use the unsafe
> function variant at the same time to take full advantage.

That said, I'm not even sure if these attributes would qualify for
debugfs_create_file_unsafe() since there's really no protection against
removal.

Overall that cocci seems a bit misleading in that it makes these changes
seem like trivial conversions. Only converting DEFINE_SIMPLE_ATTRIBUTE()
to DEFINE_DEBUGFS_ATTRIBUTE() is basically a noop, except that debugfs
has a little more overhead (for example debugfs_attr_read() wraps
simple_attr_read()), so I'm not sure if that's worth doing on its own.

Thierry

> > 
> > diff --git a/drivers/memory/tegra/tegra20-emc.c b/drivers/memory/tegra/tegra20-emc.c
> > index bd4e37b6552d..c2b4caccfae9 100644
> > --- a/drivers/memory/tegra/tegra20-emc.c
> > +++ b/drivers/memory/tegra/tegra20-emc.c
> > @@ -869,7 +869,7 @@ static int tegra_emc_debug_min_rate_set(void *data, u64 rate)
> >  	return 0;
> >  }
> >  
> > -DEFINE_SIMPLE_ATTRIBUTE(tegra_emc_debug_min_rate_fops,
> > +DEFINE_DEBUGFS_ATTRIBUTE(tegra_emc_debug_min_rate_fops,
> >  			tegra_emc_debug_min_rate_get,
> >  			tegra_emc_debug_min_rate_set, "%llu\n");
> >  
> > @@ -899,7 +899,7 @@ static int tegra_emc_debug_max_rate_set(void *data, u64 rate)
> >  	return 0;
> >  }
> >  
> > -DEFINE_SIMPLE_ATTRIBUTE(tegra_emc_debug_max_rate_fops,
> > +DEFINE_DEBUGFS_ATTRIBUTE(tegra_emc_debug_max_rate_fops,
> >  			tegra_emc_debug_max_rate_get,
> >  			tegra_emc_debug_max_rate_set, "%llu\n");
> >  
> > -- 
> > 2.27.0
> > 



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