mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-05-16 06:41:39 -04:00
Code Issues Packages Projects Releases Wiki Activity

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

Browse Source 
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: Gavin Shan <gshan@redhat.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Zeng Heng <zengheng4@huawei.com>
Tested-by: Punit Agrawal <punit.agrawal@oss.qualcomm.com>
Tested-by: Jesse Chick <jessechick@os.amperecomputing.com>
Reviewed-by: Zeng Heng <zengheng4@huawei.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
This commit is contained in:
Dave Martin
2026-03-13 14:45:59 +00:00
committed by James Morse
parent 01a0021f6c
commit 80d147d293
2 changed files with 58 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
drivers/resctrl/mpam_devices.c
View File

@@ -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);

51
drivers/resctrl/mpam_resctrl.c
View File

@@ -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)
{