linux-kernel - [PATCH 1/2] mfd: syscon: Allow using spinlocks with regmap fast

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Message-Id: <20220401135048.23245-2-angelogioacchino.delregno@collabora.com>
Date:   Fri,  1 Apr 2022 15:50:47 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     lee.jones@...aro.org
Cc:     robh+dt@...nel.org, krzk+dt@...nel.org, arnd@...db.de,
        matthias.bgg@...il.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, nfraprado@...labora.com,
        kernel@...labora.com,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Subject: [PATCH 1/2] mfd: syscon: Allow using spinlocks with regmap fast_io

On at least some SoCs accessing MMIO regions is very fast and in some
cases acquiring a mutex for every IO operation brings a significant
overhead: this is also the rationale of regmap's fast_io configuration
parameter, which makes it switch to using a spinlock instead.

Since the typical use-case for syscon is to give access to misc system
registers (not representing any specific type of device) to one or more
other drivers, and since this is done via regmap anyway, allow such
devices to let syscon configure regmap with fast_io enabled and to let
this happen, add a Devicetree property "fast-io": when this is found,
syscon will set '.fast_io = true' in the regmap config.

Of course, it makes little sense to do that if a syscon node declares
a phandle to a hardware spinlock provider node, so we check for this
property only if no hwlock is present.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
---
 drivers/mfd/syscon.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
index 191fdb87c424..3fcd9afdb9ef 100644
--- a/drivers/mfd/syscon.c
+++ b/drivers/mfd/syscon.c
@@ -101,6 +101,10 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_clk)
 		}
 	}

+	/* Checking for fast-io makes sense only if not using hwspinlock */
+	if (!syscon_config.use_hwlock && of_property_read_bool(np, "fast-io"))
+		syscon_config.fast_io = true;
+
 	syscon_config.name = kasprintf(GFP_KERNEL, "%pOFn@...x", np,
 				       (u64)res.start);
 	syscon_config.reg_stride = reg_io_width;
-- 
2.35.1