Commit 80d147d2 authored by Dave Martin's avatar Dave Martin Committed by James Morse
Browse files

arm_mpam: resctrl: Convert to/from MPAMs fixed-point formats 



MPAM uses a fixed-point formats for some hardware controls.  Resctrl
provides the bandwidth controls as a percentage. Add helpers to convert
between these.

Ensure bwa_wd is at most 16 to make it clear higher values have no meaning.

Tested-by: default avatarGavin Shan <gshan@redhat.com>
Tested-by: default avatarShaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: default avatarPeter Newman <peternewman@google.com>
Tested-by: default avatarZeng Heng <zengheng4@huawei.com>
Tested-by: default avatarPunit Agrawal <punit.agrawal@oss.qualcomm.com>
Tested-by: default avatarJesse Chick <jessechick@os.amperecomputing.com>
Reviewed-by: default avatarZeng Heng <zengheng4@huawei.com>
Reviewed-by: default avatarShaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: default avatarJonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: default avatarGavin Shan <gshan@redhat.com>
Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
Signed-off-by: default avatarBen Horgan <ben.horgan@arm.com>
Signed-off-by: default avatarJames Morse <james.morse@arm.com>
parent 01a0021f

drivers/resctrl/mpam_devices.c

+7 −0
Original line number Diff line number Diff line
@@ -713,6 +713,13 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris) 
			mpam_set_feature(mpam_feat_mbw_part, props);



		props->bwa_wd = FIELD_GET(MPAMF_MBW_IDR_BWA_WD, mbw_features);



		/*

		 * The BWA_WD field can represent 0-63, but the control fields it

		 * describes have a maximum of 16 bits.

		 */

		props->bwa_wd = min(props->bwa_wd, 16);



		if (props->bwa_wd && FIELD_GET(MPAMF_MBW_IDR_HAS_MAX, mbw_features))

			mpam_set_feature(mpam_feat_mbw_max, props);

drivers/resctrl/mpam_resctrl.c

+51 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/errno.h>

#include <linux/limits.h>

#include <linux/list.h>

#include <linux/math.h>

#include <linux/printk.h>

#include <linux/rculist.h>

#include <linux/resctrl.h>
@@ -242,6 +243,56 @@ static bool cache_has_usable_cpor(struct mpam_class *class) 
	return class->props.cpbm_wd <= 32;

}



/*

 * Each fixed-point hardware value architecturally represents a range

 * of values: the full range 0% - 100% is split contiguously into

 * (1 << cprops->bwa_wd) equal bands.

 *

 * Although the bwa_bwd fields have 6 bits the maximum valid value is 16

 * as it reports the width of fields that are at most 16 bits. When

 * fewer than 16 bits are valid the least significant bits are

 * ignored. The implied binary point is kept between bits 15 and 16 and

 * so the valid bits are leftmost.

 *

 * See ARM IHI0099B.a "MPAM system component specification", Section 9.3,

 * "The fixed-point fractional format" for more information.

 *

 * Find the nearest percentage value to the upper bound of the selected band:

 */

static u32 mbw_max_to_percent(u16 mbw_max, struct mpam_props *cprops)

{

	u32 val = mbw_max;



	val >>= 16 - cprops->bwa_wd;

	val += 1;

	val *= MAX_MBA_BW;

	val = DIV_ROUND_CLOSEST(val, 1 << cprops->bwa_wd);



	return val;

}



/*

 * Find the band whose upper bound is closest to the specified percentage.

 *

 * A round-to-nearest policy is followed here as a balanced compromise

 * between unexpected under-commit of the resource (where the total of

 * a set of resource allocations after conversion is less than the

 * expected total, due to rounding of the individual converted

 * percentages) and over-commit (where the total of the converted

 * allocations is greater than expected).

 */

static u16 percent_to_mbw_max(u8 pc, struct mpam_props *cprops)

{

	u32 val = pc;



	val <<= cprops->bwa_wd;

	val = DIV_ROUND_CLOSEST(val, MAX_MBA_BW);

	val = max(val, 1) - 1;

	val <<= 16 - cprops->bwa_wd;



	return val;

}



/* Test whether we can export MPAM_CLASS_CACHE:{2,3}? */

static void mpam_resctrl_pick_caches(void)

{