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

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 25/09/2026 14:23, Venkata Rao Kakani wrote:
> Hi Suzuki,
> 

Hi Venkat,

> Now, with this patch Host can set RMM Granule size equal to PAGE_SIZE. 
> Does RMM send the request to root to set GPT physical granule size = 
> PAGE_SIZE?

I don't think FIRME lets you do that and it would be too complex. Please
remember that the GPT is not just for the Non-secure/Realm world, but
also for the Secure world.
So, the Physical Granule size would be statically configured to 4KB on a
platform unless it supports the 4KB granule size, to support all
possible Sofware components.


> 
> In a scenario where, GPT granule size (|GPCCR_EL3|) set to 64K and Host 
> PAGE_SIZE set to 4K, how does root handle GPT granule mappings, when 
> Host send RMI_GRANULE_DELEGATE(PAGE_SIZE)?

If GPCCR_EL3 is set to 64K, RMM must not report it supports 4K GRANULE
size.

nit: Please avoid top posting your comments and use plain text for
discussions on the list.

Suzuki




> 
> 
> -- Venkat
> 
> On 24-09-2026 10:33 pm, Jonathan Cameron wrote:
>> On Thu, 24 Sep 2026 14:51:57 +0100
>> Suzuki K Poulose<suzuki.poulose@arm.com> 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@arm.com>
>>> Signed-off-by: Suzuki K Poulose<suzuki.poulose@arm.com>
>> Hi Suzuki,
>>
>> Some trivial stuff inline.  Assuming that is addressed.
>>
>> Reviewed-by: Jonathan Cameron<jonathan.cameron@oss.qualcomm.com>
>>
>>> ---
>>>   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
>>
>>
>>> +}