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

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Message-ID: <85565974d45b5553035aeabe8a98a667718482d5.camel@pengutronix.de>
Date:   Wed, 31 May 2023 20:07:43 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Sui Jingfeng <suijingfeng@...ngson.cn>,
        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

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?

> 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, so
shouldn't it be enough to simply avoid calling etnaviv_gpu_clk_get() in
the PCI device case?

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;