linux-kernel - [PATCH v9 3/4] drm/panfrost: devfreq: Disable devfreq when num

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Message-Id: <20210108091005.v9.3.I3af068abe30c9c85cabc4486385c52e56527a509@changeid>
Date:   Fri,  8 Jan 2021 09:10:10 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Cc:     fshao@...omium.org, hoegsberg@...omium.org, hsinyi@...omium.org,
        boris.brezillon@...labora.com,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v9 3/4] drm/panfrost: devfreq: Disable devfreq when num_supplies > 1

GPUs with more than a single regulator (e.g. G72 on MT8183) will
require platform-specific handling for devfreq, for 2 reasons:
 1. The opp core (drivers/opp/core.c:_generic_set_opp_regulator)
    does not support multiple regulators, so we'll need custom
    handlers.
 2. Generally, platforms with 2 regulators have platform-specific
    constraints on how the voltages should be set (e.g.
    minimum/maximum voltage difference between them), so we
    should not just create generic handlers that simply
    change the voltages without taking care of those constraints.

Disable devfreq for now on those GPUs.

Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
---

Changes in v9:
 - Explain why devfreq needs to be disabled for GPUs with >1
   regulators.

Changes in v8:
 - Use DRM_DEV_INFO instead of ERROR

Changes in v7:
 - Fix GPU ID in commit message

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..812cfecdee3b 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_INFO(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)) {
-- 
2.29.2.729.g45daf8777d-goog