[PATCH 1/3] RISC-V: Output cbom-block-size

[Andrew Jones]

On Tue, Sep 06, 2022 at 09:00:20AM +0000, Conor.Dooley at microchip.com wrote:
> On 06/09/2022 09:55, Andrew Jones wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On Tue, Sep 06, 2022 at 08:40:23AM +0000, Conor.Dooley at microchip.com wrote:
> >> On 06/09/2022 09:35, Andrew Jones wrote:
> >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >>>
> >>> Provide an info message with the block size when the Zicbom extension is
> >>> present and the block size has been determined.
> >>
> >> Why might someone care about this?
> > 
> > I was unaware of anywhere else besides hardware descriptions where this is
> > published. And, while dmesg isn't really publishing it in a way that is
> > useful to anything other than human readers either, it at least makes it
> > easy for a user to check it for sanity purposes (which is what I used it
> > for) or even for applying it if they want to write something that needs it
> > and the OS provides U-mode access to CMO.
> > 
> > I'm not married to the idea, though, so if people would rather have less
> > logs than this information, then I'm fine with dropping the patch.
> 
> I don't really care either way about logging it, if it helps people to
> be able to see it perhaps there's a better location than dmesg -
> would {debug,sys}fs be overkill?

Thinking about this some more, I think sysfs would probably be the better
way to go from the start. This patch should probably be dropped and I
can try to add a sysfs node. The hard part of that will be the naming...
How about

 /sys/devices/system/cpu/cpu*/cache/cmo_block_size

Thanks,
drew

> 
> I was just more interested in the motivation behind the change itself.
> Maybe some of the above in the commit message wuld be nice?
> 
> > 
> > Thanks,
> > drew
> > 
> >>
> >>>
> >>> Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
> >>> ---
> >>>    arch/riscv/mm/cacheflush.c | 4 +++-
> >>>    1 file changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> >>> index e5b087be1577..8595baf8e403 100644
> >>> --- a/arch/riscv/mm/cacheflush.c
> >>> +++ b/arch/riscv/mm/cacheflush.c
> >>> @@ -122,7 +122,9 @@ void riscv_init_cbom_blocksize(void)
> >>>                   }
> >>>           }
> >>>
> >>> -       if (probed_block_size)
> >>> +       if (probed_block_size) {
> >>>                   riscv_cbom_block_size = probed_block_size;
> >>> +               pr_info("riscv: Zicbom: Cache blocksize is %u bytes", probed_block_size);
> >>> +       }
> >>>    }
> >>>    #endif
> >>> --
> >>> 2.37.2
> >>>
> >>
>