Re: [PATCH 2/3] cacheinfo: Check cache properties are present in DT

[Pierre Gondois]

Hello Conor,

On 4/4/23 21:29, Conor Dooley wrote:
> Hey Pierre,
>
> On Mon, Mar 27, 2023 at 01:59:50PM +0200, Pierre Gondois wrote:
> > If a Device Tree (DT) is used, the presence of cache properties is
> > assumed. Not finding any is not considered. For arm64 platforms,
> > cache information can be fetched from the clidr_el1 register.
> > Checking whether cache information is available in the DT
> > allows to switch to using clidr_el1.
> >
> > init_of_cache_level()
> > \-of_count_cache_leaves()
> > will assume there a 2 cache leaves (L1 data/instruction caches), which
> > can be different from clidr_el1 information.
> >
> > cache_setup_of_node() tries to read cache properties in the DT.
> > If there are none, this is considered a success. Knowing no
> > information was available would allow to switch to using clidr_el1.
>
> Alex reported seeing a bunch of messages in his boot log in QEMU since
> -rc1 which appears to be the fault of, as far as I can tell, e0df442ee49
> ("cacheinfo: Check 'cache-unified' property to count cache leaves")
> like:
> cacheinfo: Unable to detect cache hierarchy for CPU N
>
> The RISC-V QEMU virt machine doesn't define any cache properties of any
> sort in the dtb, and unlike the arm64 virt machine I tried (a72) doesn't
> have some registers that cache info is discoverable from.
> When we call of_count_cache_leaves() from init_of_cache_level() and
> there are of course no reasons to increment leaves, we hit the return 2
> case you mention above, setting num_leaves to 2.
>
> As you mention, when we hit cache_setup_of_node(), levels is not going
> to be set to one, so we trigger the condition (this_leaf->level != 1)
> and, as there are no cache nodes, break out of the loop without
> incrementing index. Index is therefore less than 2, and thus we return
> -ENOENT.
> This is of course propagated back out to detect_cache_attributes() and
> triggers the "Unable to detect..." printout :(
>
> With this patch(set), the spurious error prints go away, but we are left
> with a "Early cacheinfo failed, ret = -22" which will need to be fixed.
>
> So I think this also needs to be:
> Fixes: de0df442ee49 ("cacheinfo: Check 'cache-unified' property to count cache leaves")
>
> Probably also needs a:
> Reported-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> since he's found an actual, rather than theoretical, problem!

Ok yes indeed, I will do this and the other comments you made,

Regards,
Pierre

> Cheers,
> Conor.