linux-kernel - gic700 shareability question

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Date:   Tue, 28 Mar 2023 12:48:19 +0000
From:   Peng Fan <peng.fan@....com>
To:     Marc Zyngier <maz@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: gic700 shareability question

Hi Marc,

We have an SoC that use GIC-700, but not support shareability,
Currently I just hack the code as below. Do you think it is feasible
to add firmware bindings such that these can be used to define 
the correct shareability/cacheability instead of relying on the
programmability of the CBASER register?

Saying with "broken-shareability", we just clear all the shareability
settings.

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 973ede0197e3..56c4eaf20029 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -2359,6 +2359,9 @@ static int its_setup_baser(struct its_node *its, struct its_baser *baser,
        its_write_baser(its, baser, val);
        tmp = baser->val;

+       if (tmp & GITS_BASER_SHAREABILITY_MASK)
+                       tmp &= ~GITS_BASER_SHAREABILITY_MASK;
+
        if ((val ^ tmp) & GITS_BASER_SHAREABILITY_MASK) {
                /*
                 * Shareability didn't stick. Just use
@@ -3096,6 +3099,8 @@ static void its_cpu_init_lpis(void)
        gicr_write_propbaser(val, rbase + GICR_PROPBASER);
        tmp = gicr_read_propbaser(rbase + GICR_PROPBASER);

+       tmp &= ~GICR_PROPBASER_SHAREABILITY_MASK;
+
        if ((tmp ^ val) & GICR_PROPBASER_SHAREABILITY_MASK) {
                if (!(tmp & GICR_PROPBASER_SHAREABILITY_MASK)) {
                        /*
@@ -3120,6 +3125,7 @@ static void its_cpu_init_lpis(void)
        gicr_write_pendbaser(val, rbase + GICR_PENDBASER);
        tmp = gicr_read_pendbaser(rbase + GICR_PENDBASER);

+       tmp &= ~GICR_PENDBASER_SHAREABILITY_MASK;
        if (!(tmp & GICR_PENDBASER_SHAREABILITY_MASK)) {
                /*
                 * The HW reports non-shareable, we must remove the
@@ -5094,6 +5100,7 @@ static int __init its_probe_one(struct resource *res,

        gits_write_cbaser(baser, its->base + GITS_CBASER);
        tmp = gits_read_cbaser(its->base + GITS_CBASER);
+       tmp &= ~GITS_CBASER_SHAREABILITY_MASK;

        if ((tmp ^ baser) & GITS_CBASER_SHAREABILITY_MASK) {
                if (!(tmp & GITS_CBASER_SHAREABILITY_MASK)) {

Thanks,
Peng.