Re: [PATCH v3 12/13] xen/iommu: smmu: Add Xen specific code to be able to use the driver

[Julien Grall <julien.grall@linaro.org>]

On 20/02/15 13:29, Ian Campbell wrote:
> On Mon, 2015-02-09 at 23:40 +0800, Julien Grall wrote:
>> Hi Stefano,
>>
>> On 06/02/2015 21:20, Stefano Stabellini wrote:
>>> On Fri, 30 Jan 2015, Julien Grall wrote:
>>>> -static int force_stage;
>>>> -module_param_named(force_stage, force_stage, int, S_IRUGO | S_IWUSR);
>>>> -MODULE_PARM_DESC(force_stage,
>>>> -	"Force SMMU mappings to be installed at a particular stage of translation. A value of '1' or '2' forces the corresponding stage. All other values are ignored (i.e. no stage is forced). Note that selecting a specific stage will disable support for nested translation.");
>>>
>>> for the sake of minimizing the diff, I would add
>>>
>>> #define module_param_named(a, b, c, d)
>>> #define MODULE_PARM_DESC(a, b)
>>>
>>> to the Xen definitions above
>>
>> We still have to drop force_stage because it will get unused and won't 
>> compile.
>> So it's not too bad to remove the 2 other lines.
> 
> You currently redefine it as a const int -- is it really unused?

This variable is only read to force the driver to use the specify stage
(1 or 2).

On Xen, we only want to use stage-2. The driver will bail out if the
SMMU doesn't support it.


>> All the Xen code is beginning with /* Xen: */. Though, I could add a /* 
>> Xen: End */ to make the separation clearer.
> 
> BTW, I was thinking to suggest replacing all the #if 0 with #ifndef
> CONFIG_XEN or something, which might make some of the comments shorter
> or even mean they aren't really needed.
> 
> Either way I would write it as:
>    #if 0 /* Xen: Comment comment */
> (similarly any if (0) ...)

I prefer the #if 0 /* Xen: */

>>> For the sake of minimizing the changes to Linux functions, could you
>>> write a wrapper around this function instead? That might allow you to
>>> remove the changes related to the return value.
>>
>> We should avoid to try to minimize the code against the clarity of the 
>> code...
>>
>> The change you suggest would require to modify the caller of this 
>> function, which is less clearer than this one.
> 
> Given an original function foo can you do
> 
> static void foo(void)
> {
>   original code, unmodified
> }
> static void foo_wrapper(void)
> {
>    wrapper
>    foo_orig
>    wrapper
> }
> #define foo foo_wrapper
> 
> or something along those lines?

There is some case where we need to modify the original function. So I'm
not sure it worth to add more line just for a wrapper.

Regards,


-- 
Julien Grall