Re: [PATCH v6 3/4] drm/panfrost: devfreq: Disable devfreq when num_supplies > 1

From: Steven Price <steven.price@arm.com>
To: Nicolas Boichat <drinkcat@chromium.org>,
	Rob Herring <robh@kernel.org>,
	Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Cc: hsinyi@chromium.org, hoegsberg@chromium.org, fshao@chromium.org,
	boris.brezillon@collabora.com, Daniel Vetter <daniel@ffwll.ch>,
	David Airlie <airlied@linux.ie>,
	Tomeu Vizoso <tomeu.vizoso@collabora.com>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 3/4] drm/panfrost: devfreq: Disable devfreq when num_supplies > 1
Date: Thu, 7 Jan 2021 15:59:47 +0000	[thread overview]
Message-ID: <a373044b-3e24-4e00-432f-46b0bd91b213@arm.com> (raw)
In-Reply-To: <20210105081111.v6.3.I3af068abe30c9c85cabc4486385c52e56527a509@changeid>

On 05/01/2021 00:11, Nicolas Boichat wrote:
> GPUs with more than a single regulator (e.g. G-57 on MT8183) will
> require platform-specific handling, disable devfreq for now.

Can you explain what actually goes wrong here? AFAICT the existing code 
does support controlling multiple regulators - but clearly this is the 
first platform that exercises that code with num_supplies>1.

Steve

> 
> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
> ---
> 
> Changes in v6:
>   - New change
> 
>   drivers/gpu/drm/panfrost/panfrost_devfreq.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> index f44d28fad085..1f49043aae73 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> @@ -92,6 +92,15 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
>   	struct thermal_cooling_device *cooling;
>   	struct panfrost_devfreq *pfdevfreq = &pfdev->pfdevfreq;
>   
> +	if (pfdev->comp->num_supplies > 1) {
> +		/*
> +		 * GPUs with more than 1 supply require platform-specific handling:
> +		 * continue without devfreq
> +		 */
> +		DRM_DEV_ERROR(dev, "More than 1 supply is not supported yet\n");
> +		return 0;
> +	}
> +
>   	opp_table = dev_pm_opp_set_regulators(dev, pfdev->comp->supply_names,
>   					      pfdev->comp->num_supplies);
>   	if (IS_ERR(opp_table)) {
> 