linux-kernel - Re: [PATCH v2 04/11] soc: qcom: Add Shared Memory Driver

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Date:	Tue, 21 Jul 2015 14:46:44 +0300
From:	Georgi Djakov <georgi.djakov@...aro.org>
To:	Bjorn Andersson <bjorn.andersson@...ymobile.com>
CC:	bjorn@...o.se, Kumar Gala <galak@...eaurora.org>,
	Andy Gross <agross@...eaurora.org>,
	David Brown <davidb@...eaurora.org>,
	linux-kernel@...r.kernel.org, linux-soc@...r.kernel.org,
	Jeffrey Hugo <jhugo@...eaurora.org>,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 04/11] soc: qcom: Add Shared Memory Driver

On 07/14/2015 01:27 AM, Bjorn Andersson wrote:
> On Tue 07 Jul 06:45 PDT 2015, Georgi Djakov wrote:
> 
>> Hi Bjorn,
>> Thank you for this patchset! Some nits and a question below.
>>
> 
> Thank you!
> 
>> On 06/27/2015 12:50 AM, bjorn@...o.se wrote:
>>> From: Bjorn Andersson <bjorn.andersson@...ymobile.com>
>>>
>>> This adds the Qualcomm Shared Memory Driver (SMD) providing
>>> communication channels to remote processors, ontop of SMEM.
>>>
>>> Signed-off-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
[..]
>> [...]
>>> +static int __init qcom_smd_init(void)
>>> +{
>>> +	int ret;
>>> +
>>> +	ret = bus_register(&qcom_smd_bus);
>>> +	if (ret) {
>>> +		pr_err("failed to register smd bus: %d\n", ret);
>>> +		return ret;
>>> +	}
>>> +
>>> +	return platform_driver_register(&qcom_smd_driver);
>>> +}
>>> +arch_initcall(qcom_smd_init);
>>> +
>>> +static void __exit qcom_smd_exit(void)
>>> +{
>>> +	platform_driver_unregister(&qcom_smd_driver);
>>> +	bus_unregister(&qcom_smd_bus);
>>> +}
>>> +module_exit(qcom_smd_exit);
>>> +
>> [...]
>>> +/**
>>> + * struct qcom_smd_driver - smd driver struct
>>> + * @driver:	underlying device driver
>>> + * @probe:	invoked when the smd channel is found
>>> + * @remove:	invoked when the smd channel is closed
>>> + * @callback:	invoked when an inbound message is received on the channel,
>>> + *		should return 0 on success or -EBUSY if the data cannot be
>>> + *		consumed at this time
>>> + */
>>> +struct qcom_smd_driver {
>>> +	struct device_driver driver;
>>> +	int (*probe)(struct qcom_smd_device *dev);
>>> +	void (*remove)(struct qcom_smd_device *dev);
>>> +	int (*callback)(struct qcom_smd_device *, const void *, size_t);
>>> +};
>>> +
>>> +int qcom_smd_driver_register(struct qcom_smd_driver *drv);
>>> +void qcom_smd_driver_unregister(struct qcom_smd_driver *drv);
>>> +
>>> +#define module_qcom_smd_driver(__smd_driver) \
>>> +	module_driver(__smd_driver, qcom_smd_driver_register, \
>>> +		      qcom_smd_driver_unregister)
>>> +
>>
>> This comment is mostly related to your RPM over SMD driver patch, as
>> i have a RPM clock driver based on it. The RPM clock driver registers
>> some fundamental stuff like XO and i had to hack smd-rpm to probe
>> earlier, so that most other drivers can initialize. So i was wondering,
>> what if we register the drivers on the bus earlier? What do you think?
>>
> 
> My only concern would be that if we're calling
> qcom_smd_driver_register() before the smd arch_initcall has registered
> the bus it will fail.
> 

Maybe we can use core/postcore_initcall for smd, and then arch_initcall
for smd-rpm?

> Part of this I see no problem with modifying the rpm driver to register
> earlier - and it would be good to have those regulators earlier as
> well...

Booting with initcall_debug shows me that most busses are registered at
postcore_initcall - like spmi, i2c, spi etc.

> I've intentionally not done anything about this, because it's helped to
> smoke out a bunch of EPROBE_DEFER issues for me already, but longer term
> it's not okay for all our drivers to fail 2-3 times before the
> regulators are up...

I agree. Thanks!

BR,
Georgi

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