Re: [PATCH V2 3/9] ASoC: amd: ps: add SoundWire dma driver

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

>>> +struct sdw_dma_dev_data {
>>> +	void __iomem *acp_base;
>>> +	struct mutex *acp_lock; /* used to protect acp common register access */
>>> +};
>>> +
>>>  /**
>>>   * struct acp63_dev_data - acp pci driver context
>>>   * @acp63_base: acp mmio base
>>> diff --git a/sound/soc/amd/ps/ps-sdw-dma.c b/sound/soc/amd/ps/ps-sdw-dma.c
>>> new file mode 100644
>>> index 000000000000..f41849fd035c
>>> --- /dev/null
>>> +++ b/sound/soc/amd/ps/ps-sdw-dma.c
>>> @@ -0,0 +1,70 @@
>>> +// SPDX-License-Identifier: GPL-2.0+
>>> +/*
>>> + * AMD ALSA SoC Pink Sardine SoundWire DMA Driver
>>> + *
>>> + * Copyright 2023 Advanced Micro Devices, Inc.
>>> + */
>>> +
>>> +#include <linux/err.h>
>>> +#include <linux/io.h>
>>> +#include <linux/module.h>
>>> +#include <linux/platform_device.h>
>>> +#include <sound/pcm_params.h>
>>> +#include <sound/soc.h>
>>> +#include <sound/soc-dai.h>
>>> +#include "acp63.h"
>>> +
>>> +#define DRV_NAME "amd_ps_sdw_dma"
>>> +
>>> +static const struct snd_soc_component_driver acp63_sdw_component = {
>>> +	.name		= DRV_NAME,
>>> +};
>>> +
>>> +static int acp63_sdw_platform_probe(struct platform_device *pdev)
>>> +{
>>> +	struct resource *res;
>>> +	struct sdw_dma_dev_data *sdw_data;
>>> +	int status;
>>> +
>>> +	if (!pdev->dev.platform_data) {
>>> +		dev_err(&pdev->dev, "platform_data not retrieved\n");
>>> +		return -ENODEV;
>>> +	}
>>> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>> +	if (!res) {
>>> +		dev_err(&pdev->dev, "IORESOURCE_MEM FAILED\n");
>>> +		return -ENODEV;
>>> +	}
>>> +
>>> +	sdw_data = devm_kzalloc(&pdev->dev, sizeof(*sdw_data), GFP_KERNEL);
>>> +	if (!sdw_data)
>>> +		return -ENOMEM;
>>> +
>>> +	sdw_data->acp_base = devm_ioremap(&pdev->dev, res->start, resource_size(res));
>>> +	if (!sdw_data->acp_base)
>>> +		return -ENOMEM;
>>> +
>>> +	sdw_data->acp_lock = pdev->dev.platform_data;
>> so you are sharing the same lock between parent and child platform device?
> Initially, we thought of sharing the same lock between parent and child
> platform devices. Later we have observed, mutex hang issues observed.

If the goal is a global lock, then the platform data should contain a
pointer to the lock. We used this for Intel, see .e.g. the shim_mask in
drivers/soundwire/intel_init.c, where the same pointer is used by all
children.

> 
> We have avoided critical section code and removed acp_lock from
> ACP SoundWire DMA driver while accessing ACP common registers.
> We will remove mutex lock from ACP SoundWire DMA driver code.
>> Does this work? IIRC the platform_data is copied, you do not point
>> directly to the initial data provided by the parent. We had issues with
>> SoundWire when we used platform devices, with the 'wrong' pointer used.
> Till now, we haven't observed mutex hang issues due to
> ACP PDM driver mutex lock changes.
> Agreed. We will remove the mutex code from ACP PDM driver as
> well and we will refactor code.
> In SoundWire manager driver, we are sharing the same copy for two
> manager instances. We haven't observed any issue.

What's the benefit of passing this lock as platform_data, if the goal is
to perform mutual exclusion between the two manager instances? Why not
just create the lock as part of the SoundWire probe?

If there was no need for a lock, then please remove it :-)

If it's needed, please describe what it protects, which agents rely on
it and how the lock is shared.

>>
>> The documentation does make mention of a copy....
>>
>> /**
>>  * platform_device_add_data - add platform-specific data to a platform
>> device
>>  * @pdev: platform device allocated by platform_device_alloc to add
>> resources to
>>  * @data: platform specific data for this platform device
>>  * @size: size of platform specific data
>>  *
>>  * Add a copy of platform specific data to the platform device's
>>  * platform_data pointer.  The memory associated with the platform data
>>  * will be freed when the platform device is released.
>>  */
>>> +	dev_set_drvdata(&pdev->dev, sdw_data);
>>> +	status = devm_snd_soc_register_component(&pdev->dev,
>>> +						 &acp63_sdw_component,
>>> +						 NULL, 0);
>>> +	if (status)
>>> +		dev_err(&pdev->dev, "Fail to register sdw dma component\n");
>>> +
>>> +	return status;
>>> +}