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[18/22] spi: sh-msiof: Simplify BRG's Division Ratio

Message ID 6c1085baffbdaab09115372c40a0072c5927be7a.1746180072.git.geert+renesas@glider.be
State New
Headers show
Series spi: sh-msiof: Transfer size improvements and I2S reuse | expand

Commit Message

Geert Uytterhoeven May 2, 2025, 10:13 a.m. UTC 
As FIELD_PREP() masks the value to be stored in the field, the Baud Rate
Generator's Division Ratio handling can be simplified from a look-up
table to a single subtraction.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Gcc 13.3.0 is not smart enough to consider all possible values of
div_pow in the current code, hence this works fine.
However, the simpler test loop

    for (unsigned int pow = 0; pow < 6; pow++)
	    pr_info("pow %u scr 0x%08lx\n", pow,
		    FIELD_PREP(SISCR_BRDV, (pow - 1)));

does trigger a "FIELD_PREP: value too large for the field" compile-time
assertion, unless an explicit "& FIELD_MAX(SISCR_BRDV)" is added.
Should we be pro-active and add an extra "& FIELD_MAX(SISCR_BRDV)" now,
to prepare for compilers becoming smarter?
---
 drivers/spi/spi-sh-msiof.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)
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Patch

diff --git a/drivers/spi/spi-sh-msiof.c b/drivers/spi/spi-sh-msiof.c
index 26e71fc8890fda6d..2b8c143b21219521 100644
--- a/drivers/spi/spi-sh-msiof.c
+++ b/drivers/spi/spi-sh-msiof.c
@@ -112,12 +112,6 @@  struct sh_msiof_spi_priv {
 /* SITSCR and SIRSCR */
 #define SISCR_BRPS		GENMASK(12, 8)	/* Prescaler Setting (1-32) */
 #define SISCR_BRDV		GENMASK(2, 0)	/* Baud Rate Generator's Division Ratio */
-#define SISCR_BRDV_DIV_2	0U
-#define SISCR_BRDV_DIV_4	1U
-#define SISCR_BRDV_DIV_8	2U
-#define SISCR_BRDV_DIV_16	3U
-#define SISCR_BRDV_DIV_32	4U
-#define SISCR_BRDV_DIV_1	7U
 
 /* SICTR */
 #define SICTR_TSCKIZ		GENMASK(31, 30)	/* Transmit Clock I/O Polarity Select */
@@ -256,11 +250,6 @@  static void sh_msiof_spi_reset_regs(struct sh_msiof_spi_priv *p)
 				  100);
 }
 
-static const u32 sh_msiof_spi_div_array[] = {
-	SISCR_BRDV_DIV_1, SISCR_BRDV_DIV_2, SISCR_BRDV_DIV_4,
-	SISCR_BRDV_DIV_8, SISCR_BRDV_DIV_16, SISCR_BRDV_DIV_32,
-};
-
 static void sh_msiof_spi_set_clk_regs(struct sh_msiof_spi_priv *p,
 				      struct spi_transfer *t)
 {
@@ -299,7 +288,8 @@  static void sh_msiof_spi_set_clk_regs(struct sh_msiof_spi_priv *p,
 
 	t->effective_speed_hz = parent_rate / (brps << div_pow);
 
-	scr = FIELD_PREP(SISCR_BRDV, sh_msiof_spi_div_array[div_pow]) |
+	/* div_pow == 0 maps to SISCR_BRDV_DIV_1 == all ones */
+	scr = FIELD_PREP(SISCR_BRDV, div_pow - 1) |
 	      FIELD_PREP(SISCR_BRPS, brps - 1);
 	sh_msiof_write(p, SITSCR, scr);
 	if (!(p->ctlr->flags & SPI_CONTROLLER_MUST_TX))