linux-kernel - Re: [PATCH v2 3/3] i2c / ACPI: add ACPI enumeration support

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Date:	Fri, 16 Nov 2012 14:03:57 +0100
From:	Jean Delvare <khali@...ux-fr.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	ben-linux@...ff.org, w.sang@...gutronix.de,
	linux-kernel@...r.kernel.org, lenb@...nel.org,
	rafael.j.wysocki@...el.com, broonie@...nsource.wolfsonmicro.com,
	grant.likely@...retlab.ca, linus.walleij@...aro.org,
	bhelgaas@...gle.com, mathias.nyman@...ux.intel.com,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 3/3] i2c / ACPI: add ACPI enumeration support

Hi Rafael,

On Fri, 16 Nov 2012 11:09:03 +0100, Rafael J. Wysocki wrote:
> On Thursday, November 15, 2012 01:03:17 PM Mika Westerberg wrote:
> > ACPI 5 introduced I2cSerialBus resource that makes it possible to enumerate
> > and configure the I2C slave devices behind the I2C controller. This patch
> > adds helper functions to support I2C slave enumeration.
> > 
> > An ACPI enabled I2C controller driver only needs to call acpi_i2c_register_devices()
> > in order to get its slave devices enumerated, created and bound to the
> > corresponding ACPI handle.
> > 
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> 
> Are there any objections against this patch or comments?
> 
> Worfram? Jean? Ben?

I am no longer maintaining the i2c subsystem and will not have the time
to look deeply into this. All I can say is that I very happy to see
this finally happen. Maybe with ACPI 5.0 we will finally be done with
resource conflicts plaguing many systems for several years now.

I took a quick look, and the only thing which seems suspicious is this
function:

> +static int acpi_i2c_find_child_address(struct acpi_resource *ares, void *data)
> +{
> +	struct acpi_resource_i2c_serialbus *sb;
> +	struct acpi_i2c_find *i2c_find = data;
> +
> +	if (ares->type != ACPI_RESOURCE_TYPE_SERIAL_BUS)
> +		return 1;
> +
> +	sb = &ares->data.i2c_serial_bus;
> +	if (sb->type != ACPI_RESOURCE_SERIAL_TYPE_I2C)
> +		return 1;
> +
> +	if (sb->slave_address == i2c_find->addr)

The 7-bit and 10-bit address maps overlap, so the above isn't enough.
You must compare the addresses _and_ sb->access_mode with
i2c_find->access_mode (which needs to be added and filled properly.)

> +		i2c_find->found = true;
> +
> +	return 1;
> +}

Plus, it seems odd that this function always returns 1.

-- 
Jean Delvare
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