Re: [PATCH v4 5/5] mmc: sdhci: simplify v2/v3+ clock calculation

From: Michał Mirosław
Date: Sat Aug 07 2021 - 11:40:11 EST

On Wed, Aug 04, 2021 at 03:40:38PM +0300, Adrian Hunter wrote:
> On 25/07/21 12:20 pm, Michał Mirosław wrote:
> > For base clock setting, SDHCI V2 differs from V3+ only in allowed divisor
> > values. Remove the duplicate version of code and reduce indentation
> > levels. We can see now, that 'real_div' can't be zero, so the check is
> > removed. While at it, replace divisor search loops with divide-and-clamp
> > to make the code even more readable.
>
> It doesn't seem simpler to me, just different.
>
> Simpler would mean broken into separate logical functions, getting rid of
> the gotos, and above all having the changes broken into separate patches
> for easy review.

I've extracted part of the function. It does look better I think, but it
can be improved. Please take a look.

--->8<---

mmc: sdhci: rework clock calculation

Rework the code by extracting register value and real clock rate
calculations to a separate function. This also removes duplicated
calculations of real_div and divisor search loops.

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index cfa314e659bc..9822903841f1 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1845,97 +1845,79 @@ static u16 sdhci_get_preset_value(struct sdhci_host *host)
return preset;
}

-u16 sdhci_calc_clk(struct sdhci_host *host, unsigned int clock,
+static u16 sdhci_calc_clk_mode(struct sdhci_host *host, int div, bool prog_mode,
unsigned int *actual_clock)
{
- int div = 0; /* Initialized for compiler warning */
- int real_div = div, clk_mul = 1;
+ unsigned int clk_mul, real_div;
u16 clk = 0;
- bool switch_base_clk = false;
-
- if (host->version >= SDHCI_SPEC_300) {
- if (host->preset_enabled) {
- u16 pre_val;
-
- pre_val = sdhci_get_preset_value(host);
- div = FIELD_GET(SDHCI_PRESET_SDCLK_FREQ_MASK, pre_val);
- if (pre_val & SDHCI_PRESET_CLKGEN_SEL) {
- clk = SDHCI_PROG_CLOCK_MODE;
- real_div = div + 1;
- clk_mul = host->clk_mul;
- if (!clk_mul) {
- /* The clock frequency is unknown. Assume undivided base. */
- clk_mul = 1;
- }
- } else {
- real_div = max_t(int, 1, div << 1);
- }
- goto clock_set;
- }
-
- /*
- * Check if the Host Controller supports Programmable Clock
- * Mode.
- */
- if (host->clk_mul) {
- for (div = 1; div <= 1024; div++) {
- if ((host->max_clk * host->clk_mul / div)
- <= clock)
- break;
- }
- if ((host->max_clk * host->clk_mul / div) <= clock) {
- /*
- * Set Programmable Clock Mode in the Clock
- * Control register.
- */
- clk = SDHCI_PROG_CLOCK_MODE;
- real_div = div;
- clk_mul = host->clk_mul;
- div--;
- } else {
- /*
- * Divisor can be too small to reach clock
- * speed requirement. Then use the base clock.
- */
- switch_base_clk = true;
- }
- }

- if (!host->clk_mul || switch_base_clk) {
- /* Version 3.00 divisors must be a multiple of 2. */
- if (host->max_clk <= clock) {
- div = 1;
- if (host->quirks2 & SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN)
- div = 2;
- } else {
- for (div = 2; div < SDHCI_MAX_DIV_SPEC_300;
- div += 2) {
- if ((host->max_clk / div) <= clock)
- break;
- }
- }
- real_div = div;
- div >>= 1;
- }
+ if (prog_mode) {
+ clk = SDHCI_PROG_CLOCK_MODE;
+ clk_mul = host->max_clk ?: 1;
+ real_div = div + 1;
} else {
- /* Version 2.00 divisors must be a power of 2. */
- for (div = 1; div < SDHCI_MAX_DIV_SPEC_200; div *= 2) {
- if ((host->max_clk / div) <= clock)
- break;
- }
- real_div = div;
- div >>= 1;
+ clk_mul = 1;
+ real_div = div * 2 + !div;
}

-clock_set:
- if (real_div)
- *actual_clock = (host->max_clk * clk_mul) / real_div;
+ *actual_clock = (host->max_clk * clk_mul) / real_div;
+
clk |= (div & SDHCI_DIV_MASK) << SDHCI_DIVIDER_SHIFT;
clk |= ((div & SDHCI_DIV_HI_MASK) >> SDHCI_DIV_MASK_LEN)
<< SDHCI_DIVIDER_HI_SHIFT;

return clk;
}
+
+u16 sdhci_calc_clk(struct sdhci_host *host, unsigned int clock,
+ unsigned int *actual_clock)
+{
+ unsigned int div;
+
+ if (clock == 0)
+ return 0;
+
+ if (host->preset_enabled) {
+ /* Note: Only version 3.00+ can have preset_enabled. */
+
+ u16 pre_val = sdhci_get_preset_value(host);
+ bool prog_mode = !!(pre_val & SDHCI_PRESET_CLKGEN_SEL);
+ div = FIELD_GET(SDHCI_PRESET_SDCLK_FREQ_MASK, pre_val);
+
+ return sdhci_calc_clk_mode(host, div, prog_mode, actual_clock);
+ }
+
+ if (host->version >= SDHCI_SPEC_300 && host->clk_mul) {
+ /* Programmable Clock Mode is supported. */
+
+ div = DIV_ROUND_UP(host->max_clk * host->clk_mul, clock) - 1;
+ if (div <= SDHCI_MAX_DIV_SPEC_300 / 2)
+ return sdhci_calc_clk_mode(host, div, true, actual_clock);
+
+ /*
+ * Divisor is too big for requested clock rate.
+ * Fall back to the base clock.
+ */
+ }
+
+ div = DIV_ROUND_UP(host->max_clk, clock);
+
+ if (div == 1 && (host->quirks2 & SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN))
+ div = 2;
+
+ if (host->version >= SDHCI_SPEC_300) {
+ /* Version 3.00 divisor must be 1 or a multiple of 2. */
+ if (div != 1)
+ div += div & 1;
+ div = min(div, SDHCI_MAX_DIV_SPEC_300);
+ } else {
+ /* Version 2.00 divisor must be a power of 2. */
+ div = roundup_pow_of_two(div);
+ div = min(div, SDHCI_MAX_DIV_SPEC_200);
+ }
+
+ return sdhci_calc_clk_mode(host, div / 2, false, actual_clock);
+}
EXPORT_SYMBOL_GPL(sdhci_calc_clk);

void sdhci_enable_clk(struct sdhci_host *host, u16 clk)
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index 074dc182b184..a3fa70d91410 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -284,8 +284,8 @@
* End of controller registers.
*/

-#define SDHCI_MAX_DIV_SPEC_200 256
-#define SDHCI_MAX_DIV_SPEC_300 2046
+#define SDHCI_MAX_DIV_SPEC_200 256u
+#define SDHCI_MAX_DIV_SPEC_300 2046u

/*
* Host SDMA buffer boundary. Valid values from 4K to 512K in powers of 2.