[PATCH v4 5/6] drm/ssd130x: Implement ssd130x_write_cmd() on top of ssd130x_write_cmds()

ssd130x_write_cmd() and ssd130x_write_cmds() each carried their own
regmap_write() loop over SSD13XX_COMMAND, differing only in how the caller
supplies the bytes.

Turn ssd130x_write_cmd() into a thin variadic wrapper that collects its
arguments into a small stack buffer and defers to ssd130x_write_cmds(), and
move the protocol comment onto the latter, which is where the loop now
lives.

No functional change: the bytes sent and the bus transactions used to send
them are identical for every chip on both the I2C and SPI transports.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Amit Barzilai <[email protected]>
---
 drivers/gpu/drm/solomon/ssd130x.c | 65 +++++++++++++++----------------
 1 file changed, 31 insertions(+), 34 deletions(-)

diff --git a/drivers/gpu/drm/solomon/ssd130x.c b/drivers/gpu/drm/solomon/ssd130x.c
index a229d7a87da0..61187a630a0d 100644
--- a/drivers/gpu/drm/solomon/ssd130x.c
+++ b/drivers/gpu/drm/solomon/ssd130x.c
@@ -258,41 +258,12 @@ static int ssd130x_write_data(struct ssd130x_device *ssd130x, const u8 *values,
 }
 
 /*
- * Helper to write command (SSD13XX_COMMAND). The fist variadic argument
- * is the command to write and the following are the command options.
+ * Helper to write a command (SSD13XX_COMMAND) from a buffer. The first byte
+ * is the command opcode and the following ones are its parameters.
  *
- * Note that the ssd13xx protocol requires each command and option to be
- * written as a SSD13XX_COMMAND device register value. That is why a call
- * to regmap_write(..., SSD13XX_COMMAND, ...) is done for each argument.
- */
-static int ssd130x_write_cmd(struct ssd130x_device *ssd130x, int count,
-			     /* u8 cmd, u8 option, ... */...)
-{
-	va_list ap;
-	u8 value;
-	int ret;
-
-	va_start(ap, count);
-
-	do {
-		value = va_arg(ap, int);
-		ret = regmap_write(ssd130x->regmap, SSD13XX_COMMAND, value);
-		if (ret)
-			goto out_end;
-	} while (--count);
-
-out_end:
-	va_end(ap);
-
-	return ret;
-}
-
-/*
- * Write a command byte sequence from a buffer.
- *
- * Like ssd130x_write_cmd() but takes a pre-built byte array instead of
- * variadic arguments, handy when the command is already in an array or
- * when the caller wants to use sizeof() for the length.
+ * Note that the ssd13xx protocol requires the opcode and each parameter to
+ * be written as a SSD13XX_COMMAND device register value. That is why a call
+ * to regmap_write(..., SSD13XX_COMMAND, ...) is done for each byte.
  */
 static int ssd130x_write_cmds(struct ssd130x_device *ssd130x, const u8 *cmd,
 			      size_t len)
@@ -309,6 +280,32 @@ static int ssd130x_write_cmds(struct ssd130x_device *ssd130x, const u8 *cmd,
 	return 0;
 }
 
+/*
+ * Variadic wrapper around ssd130x_write_cmds(). The first variadic argument
+ * is the command opcode and the following are its parameters.
+ *
+ * The arguments are gathered into a fixed size buffer, so at most 8 bytes
+ * can be sent per call, i.e. an opcode and seven parameters. That covers
+ * every command this driver sends through it. Commands taking more parameters,
+ * such as the grey scale tables, must use ssd130x_write_cmds() instead.
+ */
+static int ssd130x_write_cmd(struct ssd130x_device *ssd130x, int count,
+			     /* u8 cmd, u8 param, ... */...)
+{
+	u8 buf[8];
+	va_list ap;
+
+	if (drm_WARN_ON(&ssd130x->drm, count > ARRAY_SIZE(buf)))
+		return -EINVAL;
+
+	va_start(ap, count);
+	for (int i = 0; i < count; i++)
+		buf[i] = va_arg(ap, int);
+	va_end(ap);
+
+	return ssd130x_write_cmds(ssd130x, buf, count);
+}
+
 /*
  * Run a packed command sequence.  The format is a flat byte array where each
  * entry starts with a length byte followed by that many command bytes.  A
-- 
2.55.0