The optimized ICCH/ICCL values in the previous commit afterward turned
out to violate tHD;STA timing spec. We had to take into account the
fall time of SDA signal (tf) at START condition. Fix it accordingly.
With this change, sh_mobile_i2c_icch() is virtually identical to
sh_mobile_i2c_iccl(), but they're providing good descriptions of
SH-/R-Mobile I2C hardware spec, and I'd leave them as separated.
Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi.px@xxxxxxxxxxx>
---
drivers/i2c/busses/i2c-sh_mobile.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/drivers/i2c/busses/i2c-sh_mobile.c b/drivers/i2c/busses/i2c-sh_mobile.c
index 1ad80c9..4dc0cc3 100644
--- a/drivers/i2c/busses/i2c-sh_mobile.c
+++ b/drivers/i2c/busses/i2c-sh_mobile.c
@@ -203,18 +203,23 @@ static u32 sh_mobile_i2c_iccl(unsigned long count_khz, u32 tLOW, u32 tf, int off
return (((count_khz * (tLOW + tf)) + 5000) / 10000) + offset;
}
-static u32 sh_mobile_i2c_icch(unsigned long count_khz, u32 tHIGH, int offset)
+static u32 sh_mobile_i2c_icch(unsigned long count_khz, u32 tHIGH, u32 tf, int offset)
{
/*
* Conditional expression:
- * ICCH >= COUNT_CLK * tHIGH
+ * ICCH >= COUNT_CLK * (tHIGH + tf)
*
* SH-Mobile IIC hardware is aware of SCL transition period 'tr',
* and can ignore it. SH-Mobile IIC controller starts counting
* the HIGH period of the SCL signal (tHIGH) after the SCL input
* voltage increases at VIH.
+ *
+ * Afterward it turned out calculating ICCH using only tHIGH spec
+ * will result in violation of the tHD;STA timing spec. We need
+ * to take into account the fall time of SDA signal (tf) at START
+ * condition, in order to meet both tHIGH and tHD;STA specs.
*/
- return ((count_khz * tHIGH) + 5000) / 10000 + offset;
+ return (((count_khz * (tHIGH + tf)) + 5000) / 10000) + offset;
}
static void sh_mobile_i2c_init(struct sh_mobile_i2c_data *pd)
@@ -250,7 +255,7 @@ static void sh_mobile_i2c_init(struct sh_mobile_i2c_data *pd)
else
pd->icic &= ~ICIC_ICCLB8;
- pd->icch = sh_mobile_i2c_icch(i2c_clk_khz, tHIGH, offset);
+ pd->icch = sh_mobile_i2c_icch(i2c_clk_khz, tHIGH, tf, offset);
/* one more bit of ICCH in ICIC */
if ((pd->icch > 0xff) && (pd->flags & IIC_FLAG_HAS_ICIC67))
pd->icic |= ICIC_ICCHB8;
--
1.7.12.4
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