Re: [PATCH v6 10/10] arm_mpam: detect and enable MPAM-Fb PCC support

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

On Thu, 30 Jul 2026 17:25:39 +0200
Andre Przywara <andre.przywara@arm.com> wrote:

> The Arm MPAM-Fb specification [1] describes a protocol to access MSC
> registers through a firmware interface. This requires a shared memory
> region to hold the message, and a mailbox to trigger the access.
> For ACPI this is wrapped as a PCC channel, described using existing
> ACPI abstractions.
> 
> Add code to parse those PCC table descriptions associated with an MSC,
> and store the parsed information in the MSC struct.
> There can be multiple PCC channels, and each channel can serve multiple
> MSCs, so we need to keep track of the channel usage, using a list and
> a refcount.
> 
> This will be used by the MPAM-Fb access wrapper code.
> 
> [1] https://developer.arm.com/documentation/den0144/latest
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Tested-by: Ritwick Sharma <ritwick.sharma@arm.com>

One trivial thing inline.  With that resolved
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>

> ---
>  drivers/resctrl/mpam_devices.c  | 111 +++++++++++++++++++++++++++++++-
>  drivers/resctrl/mpam_fb.c       |  41 ++++++++++++
>  drivers/resctrl/mpam_internal.h |   2 +
>  3 files changed, 152 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 606ae4af2be9..8490034c7db9 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
..
> @@ -2232,7 +2317,7 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
>  static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
>  {
>  	int err;
> -	u32 tmp;
> +	u32 pcc_subspace_id;
>  	struct mpam_msc *msc;
>  	struct resource *msc_res;
>  	struct device *dev = &pdev->dev;
> @@ -2280,7 +2365,7 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
>  	if (err)
>  		return ERR_PTR(err);
>  
> -	if (device_property_read_u32(&pdev->dev, "pcc-channel", &tmp))
> +	if (device_property_read_u32(dev, "pcc-channel", &pcc_subspace_id))
>  		msc->iface = MPAM_IFACE_MMIO;
>  	else
>  		msc->iface = MPAM_IFACE_PCC;
> @@ -2296,6 +2381,28 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
>  		}
>  		msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
>  		msc->mapped_hwpage = io;
> +	} else if (msc->iface == MPAM_IFACE_PCC) {
> +		int ret;

Trivial but why not use already defined err?  


> +
> +		msc->pcc_chan = mpam_pcc_chan_get(dev, pcc_subspace_id);
> +		if (IS_ERR(msc->pcc_chan)) {
> +			pr_err("Failed to request MSC PCC channel\n");
> +			return ERR_CAST(msc->pcc_chan);
> +		}
> +
> +		ret = mpam_fb_check_shared_buffer_size(msc);
> +		if (ret) {
> +			mpam_pcc_chan_put(msc->pcc_chan);
> +
> +			return ERR_PTR(ret);
> +		}
> +
> +		ret = mpam_fb_check_protocol_version(msc);
> +		if (ret) {
> +			mpam_pcc_chan_put(msc->pcc_chan);
> +
> +			return ERR_PTR(ret);
> +		}
>  	} else {
>  		return ERR_PTR(-EINVAL);
>  	}