linux-kernel - Re: [v4 5/5] hwmon: Add Aspeed ast2600 TACH support

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Message-ID: <D5F454FE-9C4B-4B7E-8817-637D5FCC047A@aspeedtech.com>
Date:   Tue, 29 Nov 2022 07:08:36 +0000
From:   Billy Tsai <billy_tsai@...eedtech.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "lee@...nel.org" <lee@...nel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "corbet@....net" <corbet@....net>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
CC:     kernel test robot <lkp@...el.com>
Subject: Re: [v4 5/5] hwmon: Add Aspeed ast2600 TACH support

On 2022/11/23, 11:45 PM, "Guenter Roeck" <groeck7@...il.com on behalf of linux@...ck-us.net> wrote:

    On 11/22/22 22:16, Billy Tsai wrote:
    > > +The driver provides the following sensor accesses in sysfs:
    > > +=============== ======= =====================================================
    > > +fanX_input	ro	provide current fan rotation value in RPM as reported
    > > +			by the fan to the device.
    > > +fanX_div	rw	Fan divisor: Supported value are power of 4 (1, 4, 16
    > > +                        64, ... 4194304)

    > The code doesn't support 1.

The code can support 1.


    > The existence of a status register makes me wonder what is in there.
    > Does the controller report any errors ? If so, it might be worthwile
    > adding attribute(s) for it.

    > > +	if (ret)
    > > +		return ret;
    > > +
    > > +	if (!(val & TACH_ASPEED_FULL_MEASUREMENT))
    > > +		return 0;
    > > +	rpm = aspeed_tach_val_to_rpm(priv, fan_tach_ch,
    > > +				     val & TACH_ASPEED_VALUE_MASK);
    > > +
    > > +	return rpm;

The status register is the TACH_ASPEED_FULL_MEASUREMENT which is used to indicate that
the controller doesn't detect the change in tach pin for a long time.

    > > +static void aspeed_create_fan_tach_channel(struct aspeed_tach_data *priv,
    > > +					   u32 tach_ch)
    > > +{
    > > +	priv->tach_present[tach_ch] = true;
    > > +	priv->tach_channel[tach_ch].limited_inverse = 0;
    > > +	regmap_write_bits(priv->regmap, TACH_ASPEED_CTRL(tach_ch),
    > > +			  TACH_ASPEED_INVERS_LIMIT,
    > > +			  priv->tach_channel[tach_ch].limited_inverse ?
    > > +				  TACH_ASPEED_INVERS_LIMIT :
    > > +				  0);
    > > +
    > What is the purpose of the above code ? limited_inverse is always 0.

    > > +	priv->tach_channel[tach_ch].tach_debounce = DEBOUNCE_3_CLK;
    > > +	regmap_write_bits(priv->regmap, TACH_ASPEED_CTRL(tach_ch),
    > > +			  TACH_ASPEED_DEBOUNCE_MASK,
    > > +			  priv->tach_channel[tach_ch].tach_debounce
    > > +				  << TACH_ASPEED_DEBOUNCE_BIT);
    > > +
    > > +	priv->tach_channel[tach_ch].tach_edge = F2F_EDGES;
    > > +	regmap_write_bits(priv->regmap, TACH_ASPEED_CTRL(tach_ch),
    > > +			  TACH_ASPEED_IO_EDGE_MASK,
    > > +			  priv->tach_channel[tach_ch].tach_edge
    > > +				  << TACH_ASPEED_IO_EDGE_BIT);
    > > +

    > limited_inverse, tach_debounce, and tach_edge are constants.
    > There is no need to keep constants as per-channel variables.

    > > +	priv->tach_channel[tach_ch].divisor = DEFAULT_TACH_DIV;
    > > +	regmap_write_bits(priv->regmap, TACH_ASPEED_CTRL(tach_ch),
    > > +			  TACH_ASPEED_CLK_DIV_T_MASK,
    > > +			  DIV_TO_REG(priv->tach_channel[tach_ch].divisor)
    > > +				  << TACH_ASPEED_CLK_DIV_BIT);
    > > +
    > > +	priv->tach_channel[tach_ch].threshold = 0;
    > > +	regmap_write_bits(priv->regmap, TACH_ASPEED_CTRL(tach_ch),
    > > +			  TACH_ASPEED_THRESHOLD_MASK,
    > > +			  priv->tach_channel[tach_ch].threshold);
    > > +

    > The above applies to threshold as well.

The above code is used to retain the adjustable feature of the controller.
I will remove them until I add the dts property to support them.

    > > +	}
    > > +
    > > +	hwmon = devm_hwmon_device_register_with_info(dev, "aspeed_tach", priv,
    > > +						     &aspeed_tach_chip_info, NULL);
    > > +	ret = PTR_ERR_OR_ZERO(hwmon);
    > > +	if (ret)
    > > +		return dev_err_probe(dev, ret,
    > > +				     "Failed to register hwmon device\n");
    > > +	return 0;

    > Why not return the error ? Either it is an error or it isn't. If it is
    > not an error, dev_err_probe() is not appropriate. If it is, the error
    > should be returned. Either case, if this is on purpose, it needs an
    > explanation.

I have return the return value of the dev_err_probe. Did I miss someting?

Thanks

Best Regards,
Billy Tsai