linux-kernel - Re: GPU-DRM-TILCDC: Less function calls in tilcdc_convert_slave

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Date:   Fri, 23 Sep 2016 13:37:00 +0300
From:   Jyri Sarha <jsarha@...com>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
CC:     <dri-devel@...ts.freedesktop.org>, David Airlie <airlied@...ux.ie>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        <kernel-janitors@...r.kernel.org>,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: GPU-DRM-TILCDC: Less function calls in
 tilcdc_convert_slave_node() after error detection

On 09/23/16 10:36, SF Markus Elfring wrote:
>> I think the "if (node)" in the of_node_put() is there on purpose,
> 
> Yes, of course.
> 
> Does such an implementation detail correspond to a general software design pattern?
> 

Yes it does. For instance standard malloc()/free() implementation [1].

> 
>> because it potentially saves the caller one extra if()-statement
> 
> This can occasionally happen.
> 
> 
>> and keeps the caller code simpler.
> 
> A special view on software simplicity can also lead to questionable intermediate
> function implementation, can't it?
> 

I don't really follow. But in any case I do not see anything
questionable in the current tilcdc_convert_slave_node() implementation.

> 
>> Keeping the goto labels in right order needs precision
> 
> I can agree to this view.
> 
> 
>> and can lead to subtle errors.
> 
> The management of jump labels is just another software development challenge
> as usual, isn't it?
> 

Yes. But usually it pays of to avoid complexity when possible.

> 
>> Sometimes there is no way to avoid that,
> 
> How do you think about to clarify the constraints which you imagine a bit more?
> 

If the the of_node_put() behaviour would not be specified with null
pointer as parameter, there would be such a constraint.

I am beginning to have a feeling that this discussion is not going anywhere.

> 
>> but here there is.
> 
> I disagree to this conclusion.
> 
> Would you like to care a bit more for efficiency and software correctness
> around the discussed exception handling?
> 

No, I would not. I think we have reached the bottom of this discussion.
For the moment I have more important tasks to do.

Best regards,
Jyri

[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/free.html