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Subject[PATCH 4.19 23/49] i2c: meson: fixup rate calculation with filter delay
Date
From: Nicolas Belin <nbelin@baylibre.com>

commit 1334d3b4e49e35d8912a7c37ffca4c5afb9a0516 upstream.

Apparently, 15 cycles of the peripheral clock are used by the controller
for sampling and filtering. Because this was not known before, the rate
calculation is slightly off.

Clean up and fix the calculation taking this filtering delay into account.

Fixes: 30021e3707a7 ("i2c: add support for Amlogic Meson I2C controller")
Signed-off-by: Nicolas Belin <nbelin@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/i2c/busses/i2c-meson.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)

--- a/drivers/i2c/busses/i2c-meson.c
+++ b/drivers/i2c/busses/i2c-meson.c
@@ -36,10 +36,8 @@
#define REG_CTRL_ACK_IGNORE BIT(1)
#define REG_CTRL_STATUS BIT(2)
#define REG_CTRL_ERROR BIT(3)
-#define REG_CTRL_CLKDIV_SHIFT 12
-#define REG_CTRL_CLKDIV_MASK GENMASK(21, 12)
-#define REG_CTRL_CLKDIVEXT_SHIFT 28
-#define REG_CTRL_CLKDIVEXT_MASK GENMASK(29, 28)
+#define REG_CTRL_CLKDIV GENMASK(21, 12)
+#define REG_CTRL_CLKDIVEXT GENMASK(29, 28)

#define REG_SLV_ADDR GENMASK(7, 0)
#define REG_SLV_SDA_FILTER GENMASK(10, 8)
@@ -48,6 +46,7 @@
#define REG_SLV_SCL_LOW_EN BIT(28)

#define I2C_TIMEOUT_MS 500
+#define FILTER_DELAY 15

enum {
TOKEN_END = 0,
@@ -142,19 +141,21 @@ static void meson_i2c_set_clk_div(struct
unsigned long clk_rate = clk_get_rate(i2c->clk);
unsigned int div;

- div = DIV_ROUND_UP(clk_rate, freq * i2c->data->div_factor);
+ div = DIV_ROUND_UP(clk_rate, freq);
+ div -= FILTER_DELAY;
+ div = DIV_ROUND_UP(div, i2c->data->div_factor);

/* clock divider has 12 bits */
- if (div >= (1 << 12)) {
+ if (div > GENMASK(11, 0)) {
dev_err(i2c->dev, "requested bus frequency too low\n");
- div = (1 << 12) - 1;
+ div = GENMASK(11, 0);
}

- meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV_MASK,
- (div & GENMASK(9, 0)) << REG_CTRL_CLKDIV_SHIFT);
+ meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV,
+ FIELD_PREP(REG_CTRL_CLKDIV, div & GENMASK(9, 0)));

- meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT_MASK,
- (div >> 10) << REG_CTRL_CLKDIVEXT_SHIFT);
+ meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT,
+ FIELD_PREP(REG_CTRL_CLKDIVEXT, div >> 10));

/* Disable HIGH/LOW mode */
meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_EN, 0);

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