Re: [PATCH V1 1/2] soc: qcom: aoss: Expose send for generic usecase

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Fri 02 Apr 01:17 CDT 2021, Deepak Kumar Singh wrote:

> Not all upcoming usecases will have an interface to allow the aoss
> driver to hook onto. Expose the send api and create a get function to
> enable drivers to send their own messages to aoss.
> 
> Signed-off-by: Chris Lew <clew@codeaurora.org>
> Signed-off-by: Deepak Kumar Singh <deesin@codeaurora.org>
> ---
>  drivers/soc/qcom/qcom_aoss.c | 36 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/qcom/qcom_aoss.c b/drivers/soc/qcom/qcom_aoss.c
> index 53acb94..5c643f0 100644
> --- a/drivers/soc/qcom/qcom_aoss.c
> +++ b/drivers/soc/qcom/qcom_aoss.c
> @@ -8,10 +8,12 @@
>  #include <linux/io.h>
>  #include <linux/mailbox_client.h>
>  #include <linux/module.h>
> +#include <linux/of_platform.h>
>  #include <linux/platform_device.h>
>  #include <linux/pm_domain.h>
>  #include <linux/thermal.h>
>  #include <linux/slab.h>
> +#include <linux/soc/qcom/qcom_aoss.h>

I believe you forgot to 'git add' this.

>  
>  #define QMP_DESC_MAGIC			0x0
>  #define QMP_DESC_VERSION		0x4
> @@ -223,11 +225,14 @@ static bool qmp_message_empty(struct qmp *qmp)
>   *
>   * Return: 0 on success, negative errno on failure
>   */
> -static int qmp_send(struct qmp *qmp, const void *data, size_t len)
> +int qmp_send(struct qmp *qmp, const void *data, size_t len)
>  {
>  	long time_left;
>  	int ret;
>  
> +	if (!qmp || !data)

I don't see a legit use case where these are NULL, so there's probably a
developer staring at the kernel log wondering why their code isn't
working. So better wrap this in a WARN_ON() to help him/her.


Also, a developer failing to check the return value of qmp_get() would
get here with qmp being -ENODEV, -EINVAL or -EPROBE_DEFER. Which we
would gladly dereference in the next conditional. So rather than !qmp,
IS_ERR_OR_NULL(qmp) would be useful.

> +		return -EINVAL;
> +
>  	if (WARN_ON(len + sizeof(u32) > qmp->size))
>  		return -EINVAL;
>  
> @@ -261,6 +266,7 @@ static int qmp_send(struct qmp *qmp, const void *data, size_t len)
>  
>  	return ret;
>  }
> +EXPORT_SYMBOL(qmp_send);
>  
>  static int qmp_qdss_clk_prepare(struct clk_hw *hw)
>  {
> @@ -515,6 +521,34 @@ static void qmp_cooling_devices_remove(struct qmp *qmp)
>  		thermal_cooling_device_unregister(qmp->cooling_devs[i].cdev);
>  }
>  
> +/**
> + * qmp_get() - get a qmp handle from a device
> + * @dev: client device pointer
> + *
> + * Return: handle to qmp device on success, ERR_PTR() on failure
> + */
> +struct qmp *qmp_get(struct device *dev)
> +{
> +	struct platform_device *pdev;
> +	struct device_node *np;
> +	struct qmp *qmp;
> +
> +	if (!dev || !dev->of_node)
> +		return ERR_PTR(-ENODEV);

Value of @dev is an invalid argument, so I think -EINVAL is suitable.

> +
> +	np = of_parse_phandle(dev->of_node, "qcom,qmp", 0);
> +	if (!np)
> +		return ERR_PTR(-ENODEV);
> +
> +	pdev = of_find_device_by_node(np);

of_find_device_by_node() will increment the refcount of the underlying
struct device of pdev, so you need to platform_device_put() once you're
done with it.

As a side effect of not putting the struct device, the devm_kzalloc'ed
qmp pointer will remain valid. So care is needed to make sure that the
client doesn't end up with a dangling pointer if the qmp device is
removed.

My suggestion is that you add a "qmp_put()" function, which invokes
platform_device_put() and that you add some sort of tracking ("bool
orphan"?) to the struct qmp and make qmp_send() fail if this is set.

That way if someone unbinds the aoss device, the client will still have
a "valid" pointer, but won't be able to qmp_send() after qmp_close() has
been called in the aoss remove function.

Regards,
Bjorn

> +	if (!pdev)
> +		return ERR_PTR(-EINVAL);
> +
> +	qmp = platform_get_drvdata(pdev);
> +	return qmp ? qmp : ERR_PTR(-EPROBE_DEFER);
> +}
> +EXPORT_SYMBOL(qmp_get);
> +
>  static int qmp_probe(struct platform_device *pdev)
>  {
>  	struct resource *res;
> -- 
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