Hi Doug，
在 2016/5/12 9:08, David.Wu 写道:
Hi Doug,
在 2016/5/12 1:37, Doug Anderson 写道:
Hi,
On Tue, May 10, 2016 at 12:31 PM, David Wu <david.wu@xxxxxxxxxxxxxx>
wrote:
static void rk3x_i2c_adapt_div(struct rk3x_i2c *i2c, unsigned long
clk_rate)
{
struct i2c_timings *t = &i2c->t;
struct rk3x_i2c_calced_timings calc;
u64 t_low_ns, t_high_ns;
+ u32 val;
int ret;
- ret = rk3x_i2c_calc_divs(clk_rate, t, &calc);
+ ret = i2c->soc_data->calc_timings(clk_rate, t, &calc);
WARN_ONCE(ret != 0, "Could not reach SCL freq %u",
t->bus_freq_hz);
- clk_enable(i2c->clk);
+ clk_enable(i2c->pclk);
+
i2c_writel(i2c, (calc.div_high << 16) | (calc.div_low &
0xffff),
REG_CLKDIV);
- clk_disable(i2c->clk);
+
+ val = i2c_readl(i2c, REG_CON);
+ val &= ~REG_CON_TUNING_MASK;
+ val |= calc.tuning;
+ i2c_writel(i2c, val, REG_CON);
Another subtle bug here. You need to be holding the spinlock here
since you're doing a read-modify-write of a register that is also
touched by the interrupt handler. We never needed it before because
the previous register update wasn't touched by anyone else and it was
a single atomic write.
Also: technically if we are midway through a transfer when all this
happens then there will be a very short period of time when the two
timing-related registers won't match with each other. I have no idea
how much that would matter, but in the very least it seems wise to
minimize the time where they mismatch. So I'd probably write:
spin_lock_irqsave(&i2c->lock, flags);
val = i2c_readl(i2c, REG_CON);
val &= ~REG_CON_TUNING_MASK;
val |= calc.tuning;
i2c_writel(i2c, val, REG_CON);
i2c_writel(i2c, (calc.div_high << 16) | (calc.div_low & 0xffff),
REG_CLKDIV);
spin_unlock_irqrestore(&i2c->lock, flags);
...if we really end up with on a system with a dynamically changing
clock that uses the new-style timing and we see real problems, we can
always try to come up with a way to avoid any problems. Sound OK?
Good, add spin_lock is very necessary for atomic write here, thanks for
your advice.
I also found a subtle bug, it would clean the con register by use
"i2c_writel(i2c, 0, REG_CON)" in rk3x_i2c_stop(). So i think it would be
fixed by using read-modify-write way here in next version.
Otherwise, I think things look good to me. Caesar's comments would
also be good to fix.
-Doug
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