Re: [PATCH 5/5] arm_mpam: detect and enable MPAM-Fb PCC support

[Niyas Sait]

Hi Andre,

On Wed, Apr 29, 2026 at 04:13:39PM +0200, Andre Przywara wrote:

> +		msc->pcc_chan = pcc_mbox_request_channel(&msc->pcc_cl,
> +							 pcc_subspace_id);
> +		if (IS_ERR(msc->pcc_chan)) {
> +			pr_err("Failed to request MSC PCC channel\n");
> +			return (void *)msc->pcc_chan;
> +		}
> +
> +		if (msc->pcc_chan->shmem_size < MPAM_FB_MAX_MSG_SIZE) {
> +			pr_err("MPAM-Fb PCC channel size too small.\n");
> +			pcc_mbox_free_channel(msc->pcc_chan);
> +			return ERR_PTR(-ENOMEM);
> +		}

I think this allocates one PCC channel per MSC instance.

MPAM-Fb spec. allows MPAM manager to support multiple MSCs and does not
require seperate channels per MSC. Each MSC is targeted via its msc_id
in the MPAM_MSC_READ/WRITE commands.

So for systems where multiple MSC nodes point to the same PCC subspace,
should we share one pcc_mbox_chan and serialize requests through it?

Thanks,
Niyas