[External] Re: Current status of RISC-V init_cache_level()

[yunhui cui]

Hi Conor，

On Fri, Jan 19, 2024 at 4:22 PM Conor Dooley <conor.dooley at microchip.com> wrote:
>
> On Fri, Jan 19, 2024 at 10:32:38AM +0800, yunhui cui wrote:
> > On Thu, Jan 18, 2024 at 9:25 PM Conor Dooley <conor at kernel.org> wrote:
> > > On Thu, Jan 18, 2024 at 07:40:42PM +0800, yunhui cui wrote:
> > >
> > > Firstly, please don't send me off-list mails about such things
> > > and instead, please reply to the relevant threads on lkml.
> > >
> > > > There is no cache subdirectory in /sys/devices/system/cpu/cpu0/, so
> > > > lscpu cannot see the cache information. I found that the reason is
> > > > that init_cache_level() is not implemented on RISC-V.
> > >
> > > What version of the kernel are you using? I had a brief check to make
> > > sure something had not gone awry recently and I could see them on my
> > > system. What do the cpu nodes in your DT look like, assuming you are
> > > on a DT system?
> >
> > The results of top commit using linux-next on qemu, It should not
> > matter if it is combined with DT, because the following function flow
> > directly fails.
>
> Oh no, it totally does matter what the DT looks like. The default DT in
> QEMU's virt machine does not populate any cache properties. On a system
> where the DT populates these values, init_of_cache_level() will ensure
> that the correct sysfs entries are set up.
>
> > cacheinfo_sysfs_init()...init_cache_level()
> > int __weak init_cache_level(unsigned int cpu)
> > {
> > return -ENOENT;
> > }
> > Is it necessary to implement an init_cache_level() on RISC-V like other arches?
>
> In order to implement that function, we would need some mechanism for
> finding that information. Where do you suggest we get it from, if it is not
> provided to us from DT?

It's not that we don't get cache information from DT. What I want to
express is that we need to implement init_cache_level() on RISC-V,
otherwise cacheinfo_cpu_online() will return from
detect_cache_attributes() and will not execute cache_add_dev(), so it
will not be in/ sys/devices/system/cpu/cpux/ creates a "cache" node.

Thanks,
Yunhui