Due to clk rounding errors on RZ/G2L platforms, it selects a clock source
with a lower clock rate compared to a higher one.
For eg: The rounding error (533333333 Hz / 4 * 4 = 533333332 Hz < 5333333
33 Hz) selects a clk source of 400 MHz instead of 533.333333 MHz.
This patch fixes this issue by adding a margin of (1/1024) higher to
the clock rate.
Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
Tested-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
v3->v4:
* Added Tested-by tag from Wolfram.
* Updated commit description and code comment with real example.
v2->v3:
* Renamed the variable new_clock_margin->new_upper_limit in renesas_sdhi_clk_
update()
* Moved setting of new_upper_limit outside for loop.
* Updated the comment section to mention the rounding errors and merged with
existing comment out side the for loop.
* Updated commit description.
v1->v2:
* Add a comment explaining why margin is needed and set it to
that particular value.
---
drivers/mmc/host/renesas_sdhi_core.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/drivers/mmc/host/renesas_sdhi_core.c b/drivers/mmc/host/renesas_sdhi_core.c
index 6edbf5c161ab..d1b8130ee37f 100644
--- a/drivers/mmc/host/renesas_sdhi_core.c
+++ b/drivers/mmc/host/renesas_sdhi_core.c
@@ -128,6 +128,7 @@ static unsigned int renesas_sdhi_clk_update(struct tmio_mmc_host *host,
struct clk *ref_clk = priv->clk;
unsigned int freq, diff, best_freq = 0, diff_min = ~0;
unsigned int new_clock, clkh_shift = 0;
+ unsigned int new_upper_limit;
int i;
/*
@@ -153,10 +154,17 @@ static unsigned int renesas_sdhi_clk_update(struct tmio_mmc_host *host,
* greater than, new_clock. As we can divide by 1 << i for
* any i in [0, 9] we want the input clock to be as close as
* possible, but no greater than, new_clock << i.
+ *
+ * Add an upper limit of 1/1024 rate higher to the clock rate to fix
+ * clk rate jumping to lower rate due to rounding error (eg: RZ/G2L has
+ * 3 clk sources 533.333333 MHz, 400 MHz and 266.666666 MHz. The request
+ * for 533.333333 MHz will selects a slower 400 MHz due to rounding
+ * error (533333333 Hz / 4 * 4 = 533333332 Hz < 533333333 Hz)).
*/
+ new_upper_limit = (new_clock << i) + ((new_clock << i) >> 10);
for (i = min(9, ilog2(UINT_MAX / new_clock)); i >= 0; i--) {
freq = clk_round_rate(ref_clk, new_clock << i);
- if (freq > (new_clock << i)) {
+ if (freq > new_upper_limit) {
/* Too fast; look for a slightly slower option */
freq = clk_round_rate(ref_clk, (new_clock << i) / 4 * 3);
if (freq > (new_clock << i))
@@ -181,6 +189,7 @@ static unsigned int renesas_sdhi_clk_update(struct tmio_mmc_host *host,
static void renesas_sdhi_set_clock(struct tmio_mmc_host *host,
unsigned int new_clock)
{
+ unsigned int clk_margin;
u32 clk = 0, clock;
sd_ctrl_write16(host, CTL_SD_CARD_CLK_CTL, ~CLK_CTL_SCLKEN &
@@ -194,7 +203,13 @@ static void renesas_sdhi_set_clock(struct tmio_mmc_host *host,
host->mmc->actual_clock = renesas_sdhi_clk_update(host, new_clock);
clock = host->mmc->actual_clock / 512;
- for (clk = 0x80000080; new_clock >= (clock << 1); clk >>= 1)
+ /*
+ * Add a margin of 1/1024 rate higher to the clock rate in order
+ * to avoid clk variable setting a value of 0 due to the margin
+ * provided for actual_clock in renesas_sdhi_clk_update().
+ */
+ clk_margin = new_clock >> 10;
+ for (clk = 0x80000080; new_clock + clk_margin >= (clock << 1); clk >>= 1)
clock <<= 1;
/* 1/1 clock is option */
--
2.25.1
