linux-kernel - [RFC PATCH v2 29/35] irqchip/gic-v3: Don't return errors from gic_acpi_match

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Message-Id: <20230913163823.7880-30-james.morse@arm.com>
Date:   Wed, 13 Sep 2023 16:38:17 +0000
From:   James Morse <james.morse@....com>
To:     linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev
Cc:     x86@...nel.org, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: [RFC PATCH v2 29/35] irqchip/gic-v3: Don't return errors from gic_acpi_match_gicc()

gic_acpi_match_gicc() is only called via gic_acpi_count_gicr_regions().
It should only count the number of enabled redistributors, but it
also tries to sanity check the GICC entry, currently returning an
error if the Enabled bit is set, but the gicr_base_address is zero.

Adding support for the online-capable bit to the sanity check
complicates it, for no benefit. The existing check implicitly
depends on gic_acpi_count_gicr_regions() previous failing to find
any GICR regions (as it is valid to have gicr_base_address of zero if
the redistributors are described via a GICR entry).

Instead of complicating the check, remove it. Failures that happen
at this point cause the irqchip not to register, meaning no irqs
can be requested. The kernel grinds to a panic() pretty quickly.

Without the check, MADT tables that exhibit this problem are still
caught by gic_populate_rdist(), which helpfully also prints what
went wrong:
| CPU4: mpidr 100 has no re-distributor!

Signed-off-by: James Morse <james.morse@....com>
---
 drivers/irqchip/irq-gic-v3.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 72d3cdebdad1..0f54811262eb 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -2415,21 +2415,15 @@ static int __init gic_acpi_match_gicc(union acpi_subtable_headers *header,

 	/*
 	 * If GICC is enabled and has valid gicr base address, then it means
-	 * GICR base is presented via GICC
+	 * GICR base is presented via GICC. The redistributor is only known to
+	 * be accessible if the GICC is marked as enabled. If this bit is not
+	 * set, we'd need to add the redistributor at runtime, which isn't
+	 * supported.
 	 */
-	if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address) {
+	if (gicc->flags & ACPI_MADT_ENABLED && gicc->gicr_base_address)
 		acpi_data.enabled_rdists++;
-		return 0;
-	}

-	/*
-	 * It's perfectly valid firmware can pass disabled GICC entry, driver
-	 * should not treat as errors, skip the entry instead of probe fail.
-	 */
-	if (!acpi_gicc_is_usable(gicc))
-		return 0;
-
-	return -ENODEV;
+	return 0;
 }

 static int __init gic_acpi_count_gicr_regions(void)
-- 
2.39.2