Re: [PATCH v19 3/7] firmware: arm_rmm: Configure the RMM with the host's page size

[Jonathan Cameron]

On Thu, 24 Sep 2026 14:51:57 +0100
Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:

> RMM v2.0 brings the ability to set the RMM's granule size. Check the
> feature registers and configure the RMM so that it matches the host's
> page size. This means that operations can be done with a granularity
> equal to PAGE_SIZE.
> 
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Hi Suzuki,

Some trivial stuff inline.  Assuming that is addressed.

Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxxxxxxxx>

> ---
>  drivers/firmware/arm_rmm/rmi.c | 70 ++++++++++++++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
> 
> diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c
> index 3baba931f92e4..c9ea964fd9081 100644
> --- a/drivers/firmware/arm_rmm/rmi.c
> +++ b/drivers/firmware/arm_rmm/rmi.c

> +
> +static int rmi_configure(void)
> +{
> +	unsigned long granule_feature;
> +	unsigned long granule_size;
> +	int ret = 0;

Value not used.  Fine if it is future churn reduction, but I didn't spot
where if so. I'm guessing left over from refactoring

> +
> +	switch (PAGE_SIZE) {
> +	case SZ_4K:
> +		granule_size = RMI_GRANULE_SIZE_4KB;
> +		granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_4KB;
> +		break;
> +	case SZ_16K:
> +		granule_size = RMI_GRANULE_SIZE_16KB;
> +		granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_16KB;
> +		break;
> +	case SZ_64K:
> +		granule_size = RMI_GRANULE_SIZE_64KB;
> +		granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_64KB;
> +		break;
> +	default:
> +		BUILD_BUG();
> +	}
> +
> +	if (!(rmi_feat_reg(1) & granule_feature)) {
> +		pr_err("RMM does not support %luKB granules\n",
> +		       PAGE_SIZE >> 10);
> +		return -ENXIO;
> +	}
> +
> +	struct rmm_config *config __free(free_page) =
> +		(struct rmm_config *)get_zeroed_page(GFP_KERNEL);
> +
> +	if (!config) {
> +		pr_err("Unable to allocate memory for RMM config\n");
> +		return -ENOMEM;
> +	}
> +
> +	config->rmi_granule_size = granule_size;
> +
> +	/*
> +	 * For now we set the tracking_region_size to 0 which is the only option
> +	 * for 4KB PAGE_SIZE (1GB for 4KB PAGE_SIZE, 32MB/512MB for 16KB/64KB).
> +	 * TODO: Support other tracking sizes via Kconfig option for other
> +	 * PAGE_SIZES
> +	 */
> +	config->tracking_region_size = 0;
> +
> +	ret = rmi_rmm_config_set(virt_to_phys(config));
> +	if (ret) {
> +		pr_err("RMM config set failed (%d)\n", ret);
> +		ret = -EINVAL;

		return -EINVAL;

> +	}
> +
> +	return ret;
	return 0;

So obvious this is the good path without anyone having to think about it!

I did quick check on whether this was to reduce churn due to later changes
but couldn't immediately spot anything


> +}