Re: [External] [PATCH v2 4/8] riscv_cbqri: Add capacity controller probe and allocation device ops

[Drew Fustini <fustini@kernel.org>]

On Sat, Jun 27, 2026 at 05:19:44PM +0800, yunhui cui wrote:
> Hi Drew,
> 
> On Thu, Jun 25, 2026 at 9:41 AM Drew Fustini <fustini@kernel.org> wrote:
> >
> > Add support for the RISC-V CBQRI capacity controller. A platform driver
> > passes a cbqri_controller_info descriptor together with the cache level
> > to riscv_cbqri_register_cc_dt(), which probes the controller and adds it
> > to the controller list.
> >
> > Assisted-by: Claude:claude-opus-4-7
> > Co-developed-by: Adrien Ricciardi <aricciardi@baylibre.com>
> > Signed-off-by: Adrien Ricciardi <aricciardi@baylibre.com>
> > Signed-off-by: Drew Fustini <fustini@kernel.org>
> > ---
> >  MAINTAINERS                      |   3 +
> >  drivers/resctrl/Kconfig          |  13 +
> >  drivers/resctrl/Makefile         |   3 +
> >  drivers/resctrl/cbqri_devices.c  | 520 +++++++++++++++++++++++++++++++++++++++
> >  drivers/resctrl/cbqri_internal.h | 107 ++++++++
> >  include/linux/riscv_cbqri.h      |  47 ++++
> >  6 files changed, 693 insertions(+)
[..]
> > +int cbqri_apply_cache_config(struct cbqri_controller *ctrl, u32 closid,
> > +                            const struct cbqri_cc_config *cfg)
> > +{
[..]
> > +
> > +       /* Set capacity block mask (cc_block_mask) */
> > +       cbqri_set_cbm(ctrl, cfg->cbm);
> > +
> > +       /* Capacity config limit operation for the AT half implied by cfg->at */
> > +       err = cbqri_cc_alloc_op(ctrl, CBQRI_CC_ALLOC_CTL_OP_CONFIG_LIMIT,
> > +                               closid, cfg->at);
> > +       if (err < 0)
> > +               goto out;
> 
> When CUNITS=1, CONFIG_LIMIT also consumes cc_cunits. If resctrl does not
> expose unit limits, the driver should still write cc_cunits=0 before
> CONFIG_LIMIT to avoid a hidden stale/implementation-defined unit limit.
> 
> Should we handle cc_cunits here?

That is a good that cc_units should be handled even though we can't yet
expose it to resctrl. I will change the code to set cc_cunits to 0
before a config limit operation on controllers that support capacity
units, so a stale unit limit does not constrain block-mask allocation.

Thanks,
Drew