linux-kernel - Re: [PATCH v10 4/5] i2c: aspeed: added driver for Aspeed I2C

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Message-ID: <CAFd5g471kpgskO1MkBPZgFLbwAqncT_NZy=igVRkYJpxDNRVyg@mail.gmail.com>
Date:   Mon, 19 Jun 2017 21:02:46 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Wolfram Sang <wsa@...-dreams.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Joel Stanley <joel@....id.au>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Kachalov Anton <mouse@...c.ru>,
        Cédric Le Goater <clg@...d.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Ryan Chen <ryan_chen@...eedtech.com>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>
Subject: Re: [PATCH v10 4/5] i2c: aspeed: added driver for Aspeed I2C

I thought all of the comments made sense and will be addressed in my
next revision,
except the following:

>> +static int aspeed_i2c_recover_bus(struct aspeed_i2c_bus *bus)
>> +{
>> +     unsigned long time_left, flags;
>> +     int ret = 0;
>> +     u32 command;
>> +
>> +     spin_lock_irqsave(&bus->lock, flags);
>> +     command = readl(bus->base + ASPEED_I2C_CMD_REG);
>> +
>> +     if (command & ASPEED_I2CD_SDA_LINE_STS) {
>> +             /* Bus is idle: no recovery needed. */
>> +             if (command & ASPEED_I2CD_SCL_LINE_STS)
>> +                     goto out;
>> +             dev_dbg(bus->dev, "bus hung (state %x), attempting recovery\n",
>> +                     command);
>> +
>> +             reinit_completion(&bus->cmd_complete);
>> +             writel(ASPEED_I2CD_M_STOP_CMD, bus->base + ASPEED_I2C_CMD_REG);
>> +             spin_unlock_irqrestore(&bus->lock, flags);
>> +
>> +             time_left = wait_for_completion_timeout(
>> +                             &bus->cmd_complete, bus->adap.timeout);
>> +
>> +             spin_lock_irqsave(&bus->lock, flags);
>> +             if (time_left == 0)
>> +                     goto reset_out;
>> +             else if (bus->cmd_err)
>> +                     goto reset_out;
>> +             /* Recovery failed. */
>> +             else if (!(readl(bus->base + ASPEED_I2C_CMD_REG) &
>> +                        ASPEED_I2CD_SCL_LINE_STS))
>> +                     goto reset_out;
>> +     /* Bus error. */
>> +     } else {
>> +             dev_dbg(bus->dev, "bus hung (state %x), attempting recovery\n",
>> +                     command);
>
> Same dbg message as in the condition? Move it out of the 'if'?

Message is the same; that's true; however, I only want to print this
if I am actually doing
the recovery. There is a case in the first condition where we actually
don't attempt recovery.
(See both SDA and SCL high). Nevertheless, now that I am looking at
this. I think it might
make sense to make the dbg statements different since I can explain
what type of recovery
I am attempting.

>
>> +
>> +             reinit_completion(&bus->cmd_complete);
>> +             writel(ASPEED_I2CD_BUS_RECOVER_CMD,
>> +                    bus->base + ASPEED_I2C_CMD_REG);
>
> Out of interest: What does the RECOVER_CMD do?

According to the documentation, it attempts to create 1 to 8 SCL
cycles to force any stuck
device to let go of the SDA line. It then puts the hardware in a sane
state once it detects
that the bus has been recovered. I will put a comment to this effect.

>
>> +             spin_unlock_irqrestore(&bus->lock, flags);
>> +
>> +             time_left = wait_for_completion_timeout(
>> +                             &bus->cmd_complete, bus->adap.timeout);
>> +
>> +             spin_lock_irqsave(&bus->lock, flags);
>> +             if (time_left == 0)
>> +                     goto reset_out;
>> +             else if (bus->cmd_err)
>> +                     goto reset_out;
>> +             /* Recovery failed. */
>> +             else if (!(readl(bus->base + ASPEED_I2C_CMD_REG) &
>> +                        ASPEED_I2CD_SDA_LINE_STS))
>> +                     goto reset_out;
>> +     }
>> +
>> +out:
>> +     spin_unlock_irqrestore(&bus->lock, flags);
>> +
>> +     return ret;
>> +
>> +reset_out:
>> +     spin_unlock_irqrestore(&bus->lock, flags);
>> +
>> +     return aspeed_i2c_reset(bus);
>> +}

Cheers!