[PATCH v12 2/9] firmware: qcom: scm: provide a read-modify-write function

[Mukesh Ojha <quic_mojha@xxxxxxxxxxx>]

It is possible that different bits of a secure register is used
for different purpose and currently, there is no such available
function from SCM driver to do that; one similar usage was pointed
by Srinivas K. inside pinctrl-msm where interrupt configuration
register lying in secure region and written via read-modify-write
operation.

Export qcom_scm_io_rmw() to do read-modify-write operation on secure
register and reuse it wherever applicable, also document scm_lock
to convey its usage.

Suggested-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
Tested-by: Kathiravan Thirumoorthy <quic_kathirav@xxxxxxxxxxx> # IPQ9574 and IPQ5332
---
 drivers/firmware/qcom/qcom_scm.c       | 33 ++++++++++++++++++++++++++
 include/linux/firmware/qcom/qcom_scm.h |  1 +
 2 files changed, 34 insertions(+)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index 2d0ba529cf56..8f766fce5f7c 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -193,6 +193,11 @@ static void qcom_scm_bw_disable(void)
 }
 
 enum qcom_scm_convention qcom_scm_convention = SMC_CONVENTION_UNKNOWN;
+/*
+ * scm_lock to serialize call to query SMC convention and
+ * to atomically operate(read-modify-write) on different
+ * bits of secure register.
+ */
 static DEFINE_SPINLOCK(scm_lock);
 
 static enum qcom_scm_convention __get_convention(void)
@@ -481,6 +486,34 @@ static int qcom_scm_disable_sdi(void)
 	return ret ? : res.result[0];
 }
 
+int qcom_scm_io_rmw(phys_addr_t addr, unsigned int mask, unsigned int val)
+{
+	unsigned long flags;
+	unsigned int old;
+	unsigned int new;
+	int ret;
+
+	if (!__scm)
+		return -EPROBE_DEFER;
+
+	/*
+	 * Lock to atomically do rmw operation on different bits
+	 * of secure register
+	 */
+	spin_lock_irqsave(&scm_lock, flags);
+	ret = qcom_scm_io_readl(addr, &old);
+	if (ret)
+		goto unlock;
+
+	new = (old & ~mask) | (val & mask);
+
+	ret = qcom_scm_io_writel(addr, new);
+unlock:
+	spin_unlock_irqrestore(&scm_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(qcom_scm_io_rmw);
+
 static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
 {
 	struct qcom_scm_desc desc = {
diff --git a/include/linux/firmware/qcom/qcom_scm.h b/include/linux/firmware/qcom/qcom_scm.h
index ccaf28846054..3a8bb2e603b3 100644
--- a/include/linux/firmware/qcom/qcom_scm.h
+++ b/include/linux/firmware/qcom/qcom_scm.h
@@ -82,6 +82,7 @@ bool qcom_scm_pas_supported(u32 peripheral);
 
 int qcom_scm_io_readl(phys_addr_t addr, unsigned int *val);
 int qcom_scm_io_writel(phys_addr_t addr, unsigned int val);
+int qcom_scm_io_rmw(phys_addr_t addr, unsigned int mask, unsigned int val);
 
 bool qcom_scm_restore_sec_cfg_available(void);
 int qcom_scm_restore_sec_cfg(u32 device_id, u32 spare);
-- 
2.43.0.254.ga26002b62827