linux-kernel - Re: [PATCH 01/21] of: device: Support loading a module with OF based modalias

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Date:	Mon, 27 Jun 2016 21:17:50 -0700
From:	Bjorn Andersson <bjorn.andersson@...aro.org>
To:	Stephen Boyd <stephen.boyd@...aro.org>
Cc:	linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	Andy Gross <andy.gross@...aro.org>,
	Neil Armstrong <narmstrong@...libre.com>,
	Arnd Bergmann <arnd@...db.de>, Felipe Balbi <balbi@...nel.org>,
	Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH 01/21] of: device: Support loading a module with OF based
 modalias

On Sun 26 Jun 00:28 PDT 2016, Stephen Boyd wrote:

> In the case of ULPI devices, we want to be able to load the
> driver before registering the device so that we don't get stuck
> in a loop waiting for the phy module to appear and failing usb
> controller probe. Currently we request the ulpi module via the
> ulpi ids, but in the DT case we might need to request it with the
> OF based modalias instead. Add a common function that allows
> anyone to request a module with the OF based modalias.
> 
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: <devicetree@...r.kernel.org>
> Signed-off-by: Stephen Boyd <stephen.boyd@...aro.org>
> ---
>  drivers/of/device.c       | 50 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/of_device.h |  6 ++++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index fd5cfad7c403..f275e5beb736 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -226,6 +226,56 @@ ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len)
>  	return tsize;
>  }
>  
> +static ssize_t of_device_modalias_size(struct device *dev)
> +{
> +	const char *compat;
> +	int cplen, i;
> +	ssize_t csize;
> +
> +	if ((!dev) || (!dev->of_node))
> +		return -ENODEV;
> +
> +	/* Name & Type */
> +	csize = 5 + strlen(dev->of_node->name) + strlen(dev->of_node->type);

It would be clearer if you replaced 5 with strlen("of:NT"), but...

> +
> +	/* Get compatible property if any */
> +	compat = of_get_property(dev->of_node, "compatible", &cplen);
> +	if (!compat)
> +		return csize;
> +
> +	/* Find true end (we tolerate multiple \0 at the end */
> +	for (i = (cplen - 1); i >= 0 && !compat[i]; i--)
> +		cplen--;
> +	if (!cplen)
> +		return csize;
> +	cplen++;
> +
> +	/* Check space (need cplen+1 chars including final \0) */
> +	return csize + cplen;
> +}

...if I understand of_device_get_modalias() correctly you should be able
to replace this function with:

  size = of_device_get_modalias(dev, NULL, 0);

snprintf() will not write to NULL, csize will be larger than 0 so tsize
will be returned before it will memcpy() to the buffer.

> +
> +int of_device_request_module(struct device *dev)
> +{
> +	char *str;
> +	ssize_t size;
> +	int ret;
> +
> +	size = of_device_modalias_size(dev);
> +	if (size < 0)
> +		return size;
> +
> +	str = kmalloc(size + 1, GFP_KERNEL);
> +	if (!str)
> +		return -ENOMEM;
> +
> +	of_device_get_modalias(dev, str, size);
> +	str[size] = '\0';
> +	ret = request_module(str);
> +	kfree(str);
> +
> +	return ret;
> +}
> +

Regards,
Bjorn