linux-kernel - Re: [PATCH v2] ACPI: surface3_power: MSHW0011 rev-eng implementation

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Date:   Sat, 1 Jul 2017 02:47:32 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Julia Lawall <julia.lawall@...6.fr>
Cc:     Bastien Nocera <hadess@...ess.net>,
        Stephen Just <stephenjust@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Lv Zheng <lv.zheng@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-acpi@...r.kernel.org, devel@...ica.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ACPI: surface3_power: MSHW0011 rev-eng implementation

Hi,

On Thu, Jun 29, 2017 at 02:10:09PM +0200, Benjamin Tissoires wrote:
> [...]
>
> +	/* get design capacity */
> +	ret = i2c_smbus_read_word_data(client,
> +				       MSHW0011_BAT0_REG_DESIGN_CAPACITY);
> +	if (ret < 0) {
> +		dev_err(&client->dev, "Error reading design capacity: %d\n",
> +			ret);
> +		return ret;
> +	}
> +	bix->design_capacity = le16_to_cpu(ret);

i2c_smbus_read_word_data() returns native endianess for
little-endian bus (it basically has builtin le16_to_cpu).
Your conversion actually _breaks_ support on big endian
machines by converting it back.

That seems to be a common mistake in the kernel and it
might be a good idea to add some Coccinelle script for
it?

-- Sebastian

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