Re: [PATCH 1/2] coresight: Set affinity to invalid for missing CPU phandle

[Sai Prakash Ranjan]

Hi Suzuki,

Thanks for the review.

On 6/20/2019 7:25 PM, Suzuki K Poulose wrote:
> Sai,
>
> Thanks for the patch. Please could you change the subject to :
>
> "coresight: Do not default to CPU0 for missing CPU phandle"

Sure.

> On 20/06/2019 14:45, Sai Prakash Ranjan wrote:
> > Affinity defaults to CPU0 in case of missing CPU phandle
> > and this leads to crashes in some cases because of such
> > wrong assumption. Fix this by returning -ENODEV in
>
> Thats not the right justification. Causing crashes is due to
> bad DT/firmware. I would be happy with something like :
>
> "Coresight platform support assumes that a missing \"cpu\" phandle
> defaults to CPU0. This could be problematic and unnecessarily binds
> components to CPU0, where they may not be. Let us make the DT binding
> rules a bit stricter by not defaulting to CPU0 for missing "cpu"
> affinity information."
>
> Also, you must
>
> 1) update the devicetree/bindings document to reflect the same.
> 2) update the drivers to take appropriate action on the missing CPU
>  ÂÂ where they are expected (e.g, CPU-debug, etm*), to prevent
>  ÂÂ breaking a bisect.

Sure will do it and repost.

> > coresight platform for such cases and then handle it
> > in the coresight drivers.
> >
> > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> > ---
> > Â drivers/hwtracing/coresight/coresight-platform.c | 10 ++++++----
> > Â 1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-platform.c 
> > b/drivers/hwtracing/coresight/coresight-platform.c
> > index 3c5ceda8db24..b1ea60c210e1 100644
> > --- a/drivers/hwtracing/coresight/coresight-platform.c
> > +++ b/drivers/hwtracing/coresight/coresight-platform.c
> > @@ -160,15 +160,17 @@ static int of_coresight_get_cpu(struct device *dev)
> > ÂÂÂÂÂ if (!dev->of_node)
> > ÂÂÂÂÂÂÂÂÂ return 0;
> > +
> > ÂÂÂÂÂ dn = of_parse_phandle(dev->of_node, "cpu", 0);
> > -ÂÂÂ /* Affinity defaults to CPU0 */
> > +
> > +ÂÂÂ /* Affinity defaults to invalid if no cpu nodes are found*/
>
> The code is self explanatory here. You could drop the comment.

Sure.

> > ÂÂÂÂÂ if (!dn)
> > -ÂÂÂÂÂÂÂ return 0;
> > +ÂÂÂÂÂÂÂ return -ENODEV;
> > +
> > ÂÂÂÂÂ cpu = of_cpu_node_to_id(dn);
> > ÂÂÂÂÂ of_node_put(dn);
> > -ÂÂÂ /* Affinity to CPU0 if no cpu nodes are found */
> > -ÂÂÂ return (cpu < 0) ? 0 : cpu;
> > +ÂÂÂ return cpu;
> > Â }
>
> Suzuki

-Sai

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