Re: [PATCH v3 09/16] arm_mpam: let low level MSC write accessors return an error

[Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>]

On Fri, 10 Jul 2026 16:45:13 +0200
Andre Przywara <andre.przywara@arm.com> wrote:

> The upcoming MPAM-Fb support does not use MMIO primitives to access an
> MSC, but employs a shared-memory/doorbell based firmware protocol.
> Its complexity means that is must be able to handle errors, whereas we
> always assume an MSC access succeeds today.
> 
> Change the __mpam_write_reg() low level accessor function to return an
> error code. At the moment this is always 0, but this will change with
> alternative MSC access methods.
> 
> Also change some low level wrappers to propagate the error.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
I mentioned earlier that to me a split of read vs write into different
series of patches is making things more complex than they might be.
They are same 'sort' of change so I'd do them together.

Then a reviewer can quickly see if all new sources of error are
covered.

Thanks (and sorry I didn't look at v2!)

Jonathan

> ---
>  drivers/resctrl/mpam_devices.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index b2ecaba29fcc..f1e40ce24f5a 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -195,18 +195,20 @@ static inline int _mpam_read_partsel_reg(struct mpam_msc *msc, u16 reg,
>  
>  #define mpam_read_partsel_reg(msc, reg, res) _mpam_read_partsel_reg(msc, MPAMF_##reg, res)
>  
> -static void __mpam_write_reg(struct mpam_msc *msc, u16 reg, u32 val)
> +static int __mpam_write_reg(struct mpam_msc *msc, u16 reg, u32 val)
>  {
>  	WARN_ON_ONCE(reg + sizeof(u32) > msc->mapped_hwpage_sz);
>  	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
>  
>  	writel_relaxed(val, msc->mapped_hwpage + reg);
> +
> +	return 0;
>  }
>  
> -static inline void _mpam_write_partsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
> +static inline int _mpam_write_partsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
>  {
>  	lockdep_assert_held_once(&msc->part_sel_lock);
> -	__mpam_write_reg(msc, reg, val);
> +	return __mpam_write_reg(msc, reg, val);
>  }
>  
>  #define mpam_write_partsel_reg(msc, reg, val)  _mpam_write_partsel_reg(msc, MPAMCFG_##reg, val)
> @@ -220,10 +222,10 @@ static inline int _mpam_read_monsel_reg(struct mpam_msc *msc, u16 reg,
>  
>  #define mpam_read_monsel_reg(msc, reg, res) _mpam_read_monsel_reg(msc, MSMON_##reg, res)
>  
> -static inline void _mpam_write_monsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
> +static inline int _mpam_write_monsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
>  {
>  	mpam_mon_sel_lock_held(msc);
> -	__mpam_write_reg(msc, reg, val);
> +	return __mpam_write_reg(msc, reg, val);
>  }
>  
>  #define mpam_write_monsel_reg(msc, reg, val)   _mpam_write_monsel_reg(msc, MSMON_##reg, val)