regmap: Add regmap_read_bypassed()

[ Upstream commit 70ee853eec5693fefd8348a2b049d9cb83362e58 ]

Add a regmap_read_bypassed() to allow reads from the hardware registers
while the regmap is in cache-only mode.

A typical use for this is to keep the cache in cache-only mode until
the hardware has reached a valid state, but one or more status registers
must be polled to determine when this state is reached.

For example, firmware download on the cs35l56 can take several seconds if
there are multiple amps sharing limited bus bandwidth. This is too long
to block in probe() so it is done as a background task. The device must
be soft-reset to reboot the firmware and during this time the registers are
not accessible, so the cache should be in cache-only. But the driver must
poll a register to detect when reboot has completed.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: 8a731fd37f8b ("ASoC: cs35l56: Move utility functions to shared file")
Link: https://msgid.link/r/20240408101803.43183-2-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index ea6157747199..c5b5241891a5 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -2837,6 +2837,43 @@ int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val)
 EXPORT_SYMBOL_GPL(regmap_read);
 
 /**
+ * regmap_read_bypassed() - Read a value from a single register direct
+ *			    from the device, bypassing the cache
+ *
+ * @map: Register map to read from
+ * @reg: Register to be read from
+ * @val: Pointer to store read value
+ *
+ * A value of zero will be returned on success, a negative errno will
+ * be returned in error cases.
+ */
+int regmap_read_bypassed(struct regmap *map, unsigned int reg, unsigned int *val)
+{
+	int ret;
+	bool bypass, cache_only;
+
+	if (!IS_ALIGNED(reg, map->reg_stride))
+		return -EINVAL;
+
+	map->lock(map->lock_arg);
+
+	bypass = map->cache_bypass;
+	cache_only = map->cache_only;
+	map->cache_bypass = true;
+	map->cache_only = false;
+
+	ret = _regmap_read(map, reg, val);
+
+	map->cache_bypass = bypass;
+	map->cache_only = cache_only;
+
+	map->unlock(map->lock_arg);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(regmap_read_bypassed);
+
+/**
  * regmap_raw_read() - Read raw data from the device
  *
  * @map: Register map to read from