linux-kernel - Re: [PATCH v6 2/6] drm/etnaviv: add a dedicated function to get various clocks

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Date:   Thu, 1 Jun 2023 18:09:24 +0800
From:   Sui Jingfeng <suijingfeng@...ngson.cn>
To:     Lucas Stach <l.stach@...gutronix.de>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-kernel@...r.kernel.org, etnaviv@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v6 2/6] drm/etnaviv: add a dedicated function to get
 various clocks

Hi,

On 2023/6/1 02:07, Lucas Stach wrote:
> Am Mittwoch, dem 31.05.2023 um 00:06 +0800 schrieb Sui Jingfeng:
>> Because it is also platform-dependent, there are environments where don't
>> have CLK subsystem support, for example, discreted PCI gpu. So don't rage
>> quit if there is no CLK subsystem.
>>
>> For the GPU in LS7a1000 and LS2k2000, the working frequency of the GPU is
>> tuned by configuring the PLL register directly.
>>
> Is this PLL under control of system firmware and invisible to Linux?
Yes, it is registers, both system firmware and kernel space driver can 
access it.
>> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
>> ---
>>   drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 62 ++++++++++++++++++---------
>>   drivers/gpu/drm/etnaviv/etnaviv_gpu.h |  1 +
>>   2 files changed, 42 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
>> index 636d3f39ddcb..4937580551a5 100644
>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
>> @@ -1565,10 +1565,45 @@ static irqreturn_t irq_handler(int irq, void *data)
>>   	return ret;
>>   }
>>   
>> +static int etnaviv_gpu_clk_get(struct etnaviv_gpu *gpu)
>> +{
>> +	struct device *dev = gpu->dev;
>> +
>> +	if (gpu->no_clk)
>> +		return 0;
>> +
>> +	gpu->clk_reg = devm_clk_get_optional(dev, "reg");
>> +	DBG("clk_reg: %p", gpu->clk_reg);
>> +	if (IS_ERR(gpu->clk_reg))
>> +		return PTR_ERR(gpu->clk_reg);
>> +
>> +	gpu->clk_bus = devm_clk_get_optional(dev, "bus");
>> +	DBG("clk_bus: %p", gpu->clk_bus);
>> +	if (IS_ERR(gpu->clk_bus))
>> +		return PTR_ERR(gpu->clk_bus);
>> +
>> +	gpu->clk_core = devm_clk_get(dev, "core");
>> +	DBG("clk_core: %p", gpu->clk_core);
>> +	if (IS_ERR(gpu->clk_core))
>> +		return PTR_ERR(gpu->clk_core);
>> +	gpu->base_rate_core = clk_get_rate(gpu->clk_core);
>> +
>> +	gpu->clk_shader = devm_clk_get_optional(dev, "shader");
>> +	DBG("clk_shader: %p", gpu->clk_shader);
>> +	if (IS_ERR(gpu->clk_shader))
>> +		return PTR_ERR(gpu->clk_shader);
>> +	gpu->base_rate_shader = clk_get_rate(gpu->clk_shader);
>> +
>> +	return 0;
>> +}
>> +
>>   static int etnaviv_gpu_clk_enable(struct etnaviv_gpu *gpu)
>>   {
>>   	int ret;
>>   
>> +	if (gpu->no_clk)
>> +		return 0;
>> +
> I don't see why this would be needed? If your platform doesn't provide
> CONFIG_HAVE_CLK all those functions should be successful no-ops, so
> there is no need to special case this in the driver.
>
> Or does your platform in fact provide a clk subsystem, just the GPU
> clocks are managed by it?
>
> Also all those functions are fine with being called on a NULL clk,
right
> so
> shouldn't it be enough to simply avoid calling etnaviv_gpu_clk_get() in
> the PCI device case?

Yes, I just tried, your are right.

There also no need to add the 'no_clk' member into struct etnaviv_gpu

> Regards,
> Lucas
>
>>   	ret = clk_prepare_enable(gpu->clk_reg);
>>   	if (ret)
>>   		return ret;
>> @@ -1599,6 +1634,9 @@ static int etnaviv_gpu_clk_enable(struct etnaviv_gpu *gpu)
>>   
>>   static int etnaviv_gpu_clk_disable(struct etnaviv_gpu *gpu)
>>   {
>> +	if (gpu->no_clk)
>> +		return 0;
>> +
>>   	clk_disable_unprepare(gpu->clk_shader);
>>   	clk_disable_unprepare(gpu->clk_core);
>>   	clk_disable_unprepare(gpu->clk_bus);
>> @@ -1865,27 +1903,9 @@ static int etnaviv_gpu_platform_probe(struct platform_device *pdev)
>>   		return err;
>>   
>>   	/* Get Clocks: */
>> -	gpu->clk_reg = devm_clk_get_optional(&pdev->dev, "reg");
>> -	DBG("clk_reg: %p", gpu->clk_reg);
>> -	if (IS_ERR(gpu->clk_reg))
>> -		return PTR_ERR(gpu->clk_reg);
>> -
>> -	gpu->clk_bus = devm_clk_get_optional(&pdev->dev, "bus");
>> -	DBG("clk_bus: %p", gpu->clk_bus);
>> -	if (IS_ERR(gpu->clk_bus))
>> -		return PTR_ERR(gpu->clk_bus);
>> -
>> -	gpu->clk_core = devm_clk_get(&pdev->dev, "core");
>> -	DBG("clk_core: %p", gpu->clk_core);
>> -	if (IS_ERR(gpu->clk_core))
>> -		return PTR_ERR(gpu->clk_core);
>> -	gpu->base_rate_core = clk_get_rate(gpu->clk_core);
>> -
>> -	gpu->clk_shader = devm_clk_get_optional(&pdev->dev, "shader");
>> -	DBG("clk_shader: %p", gpu->clk_shader);
>> -	if (IS_ERR(gpu->clk_shader))
>> -		return PTR_ERR(gpu->clk_shader);
>> -	gpu->base_rate_shader = clk_get_rate(gpu->clk_shader);
>> +	err = etnaviv_gpu_clk_get(gpu);
>> +	if (err)
>> +		return err;
>>   
>>   	/* TODO: figure out max mapped size */
>>   	dev_set_drvdata(dev, gpu);
>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
>> index 98c6f9c320fc..6da5209a7d64 100644
>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
>> @@ -148,6 +148,7 @@ struct etnaviv_gpu {
>>   	struct clk *clk_reg;
>>   	struct clk *clk_core;
>>   	struct clk *clk_shader;
>> +	bool no_clk;
>>   
>>   	unsigned int freq_scale;
>>   	unsigned long base_rate_core;

-- 
Jingfeng