linux-kernel - Re: [PATCH v5 08/11] powerpc/pseries/iommu: Update remove_dma

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Date:   Tue, 24 Aug 2021 16:31:41 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Leonardo Brás <leobras.c@...il.com>,
        Frederic Barrat <fbarrat@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        David Gibson <david@...son.dropbear.id.au>,
        kernel test robot <lkp@...el.com>,
        Nicolin Chen <nicoleotsuka@...il.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 08/11] powerpc/pseries/iommu: Update
 remove_dma_window() to accept property name



On 17/08/2021 16:12, Leonardo Brás wrote:
> On Tue, 2021-08-17 at 02:59 -0300, Leonardo Brás wrote:
>> Hello Fred, thanks for the feedback!
>>
>> On Tue, 2021-07-20 at 19:51 +0200, Frederic Barrat wrote:
>>>
>>>
>>> On 16/07/2021 10:27, Leonardo Bras wrote:
>>>> Update remove_dma_window() so it can be used to remove DDW with a
>>>> given
>>>> property name.
>>>>
>>>> This enables the creation of new property names for DDW, so we
>>>> can
>>>> have different usage for it, like indirect mapping.
>>>>
>>>> Signed-off-by: Leonardo Bras <leobras.c@...il.com>
>>>> Reviewed-by: Alexey Kardashevskiy <aik@...abs.ru>
>>>> ---
>>>>    arch/powerpc/platforms/pseries/iommu.c | 21 +++++++++++--------
>>>> --
>>>>    1 file changed, 11 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/arch/powerpc/platforms/pseries/iommu.c
>>>> b/arch/powerpc/platforms/pseries/iommu.c
>>>> index 108c3dcca686..17c6f4706e76 100644
>>>> --- a/arch/powerpc/platforms/pseries/iommu.c
>>>> +++ b/arch/powerpc/platforms/pseries/iommu.c
>>>> @@ -830,31 +830,32 @@ static void remove_dma_window(struct
>>>> device_node *np, u32 *ddw_avail,
>>>>                          np, ret,
>>>> ddw_avail[DDW_REMOVE_PE_DMA_WIN],
>>>> liobn);
>>>>    }
>>>>    
>>>> -static void remove_ddw(struct device_node *np, bool remove_prop)
>>>> +static int remove_ddw(struct device_node *np, bool remove_prop,
>>>> const char *win_name)
>>>>    {
>>>
>>>
>>> Why switch to returning an int? None of the callers check it.
>>
>> IIRC, in a previous version it did make sense, which is not the case
>> anymore. I will revert this.
>>
>> Thanks!
> 
> Oh, sorry about that, it is in fact still needed:


Then you should have added it in 10/11.

> 
> It will make sense in patch v5 10/11:
> On iommu_reconfig_notifier(), if (action == OF_RECONFIG_DETACH_NODE),
> we need to remove a DDW if it exists.
> 
> As there may be different window names, it tests for DIRECT64_PROPNAME,
> and if it's not found, it tests for DMA64_PROPNAME.
> 
> This approach will skip scanning for DMA64_PROPNAME if
> DIRECT64_PROPNAME was found, as both may not exist in the same node.
> But for this approach to work we need remove_ddw() to return error if
> the property is not found.
> 
> Does it make sense? or should I just test for both?

Or you could just try removing both without checking the return code, it 
is one extra of_find_property in very rare code path. Not worth 
reposting though imho. (sorry I was off last week, catching up). Thanks,



-- 
Alexey