[PATCH 2/2] rtc: driver for Conexant Digicolor CX92755 on-chip RTC

[Andrew Morton]

On Mon, 23 Mar 2015 15:28:54 +0200 Baruch Siach <baruch at tkos.co.il> wrote:

> Add driver for the RTC hardware block on the Conexant CX92755 SoC, from the
> Digicolor series of SoCs. Tested on the Equinox evaluation board for the
> CX92755 chip.
> 
> ...
>
> +static int dc_rtc_read(struct dc_rtc *rtc, unsigned long *val)
> +{
> +	u8 read_cmds[] = {CMD_READ, CMD_NOP};
> +	u32 reference, time1, time2;
> +	int ret;
> +
> +	ret = dc_rtc_cmds(rtc, read_cmds, ARRAY_SIZE(read_cmds));

This is asking the compiler to build read_cmds[] on the stack each time
dc_rtc_read() is called.

If we instead create the array at compile time:

+++ a/drivers/rtc/rtc-digicolor.c
@@ -42,7 +42,7 @@ struct dc_rtc {
 	void __iomem		*regs;
 };
 
-static int dc_rtc_cmds(struct dc_rtc *rtc, u8 *cmds, int len)
+static int dc_rtc_cmds(struct dc_rtc *rtc, const u8 *cmds, int len)
 {
 	u8 val;
 	int i, ret;
@@ -62,7 +62,7 @@ static int dc_rtc_cmds(struct dc_rtc *rt
 
 static int dc_rtc_read(struct dc_rtc *rtc, unsigned long *val)
 {
-	u8 read_cmds[] = {CMD_READ, CMD_NOP};
+	static const u8 read_cmds[] = {CMD_READ, CMD_NOP};
 	u32 reference, time1, time2;
 	int ret;
 
@@ -86,7 +86,7 @@ static int dc_rtc_read(struct dc_rtc *rt
 
 static int dc_rtc_write(struct dc_rtc *rtc, u32 val)
 {
-	u8 write_cmds[] = {CMD_WRITE, CMD_NOP, CMD_RESET, CMD_NOP};
+	static const u8 write_cmds[] = {CMD_WRITE, CMD_NOP, CMD_RESET, CMD_NOP};
 
 	writel_relaxed(val, rtc->regs + DC_RTC_REFERENCE);
 	return dc_rtc_cmds(rtc, write_cmds, ARRAY_SIZE(write_cmds));

The code gets a bit smaller and faster:

   text    data     bss     dec     hex filename
   1628     400     512    2540     9ec drivers/rtc/rtc-digicolor.o-before
   1593     400     536    2529     9e1 drivers/rtc/rtc-digicolor.o-after