From mboxrd@z Thu Jan 1 00:00:00 1970 From: david.wu@rock-chips.com (David.Wu) Date: Thu, 12 May 2016 23:07:34 +0800 Subject: [PATCH v8 7/8] i2c: rk3x: add i2c support for rk3399 soc In-Reply-To: <5733D7AA.1060500@rock-chips.com> References: <1462908252-27016-1-git-send-email-david.wu@rock-chips.com> <1462908698-27284-1-git-send-email-david.wu@rock-chips.com> <5733D7AA.1060500@rock-chips.com> Message-ID: <57349C36.4030401@rock-chips.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Doug? ? 2016/5/12 9:08, David.Wu ??: > Hi Doug, > > ? 2016/5/12 1:37, Doug Anderson ??: >> Hi, >> >> On Tue, May 10, 2016 at 12:31 PM, David Wu >> 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 >> >> >>