linux-kernel - Re: [PATCH v2 10/15] drm: sprd: add clock gating support

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Message-ID: <aICeC5lSSW0qR7oh@abscue.de>
Date: Wed, 23 Jul 2025 10:32:11 +0200
From: Otto Pflüger <otto.pflueger@...cue.de>
To: Maxime Ripard <mripard@...nel.org>
Cc: David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Orson Zhai <orsonzhai@...il.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Chunyan Zhang <zhang.lyra@...il.com>,
	Kevin Tang <kevin.tang@...soc.com>, dri-devel@...ts.freedesktop.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 10/15] drm: sprd: add clock gating support

Hi Maxime,

On Wed, Jul 23, 2025 at 09:00:28AM +0200, Maxime Ripard wrote:
> Hi,
> 
> On Tue, Jul 22, 2025 at 04:41:12PM +0200, Otto Pflüger wrote:
> > Enable the DPU and DSI clocks specified in the device tree.
> > Disable the DSI clock when it is not needed.
> > 
> > Signed-off-by: Otto Pflüger <otto.pflueger@...cue.de>
> > ---
> >  drivers/gpu/drm/sprd/sprd_dpu.c | 7 +++++++
> >  drivers/gpu/drm/sprd/sprd_dpu.h | 1 +
> >  drivers/gpu/drm/sprd/sprd_dsi.c | 9 +++++++++
> >  drivers/gpu/drm/sprd/sprd_dsi.h | 4 +++-
> >  4 files changed, 20 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/sprd/sprd_dpu.c b/drivers/gpu/drm/sprd/sprd_dpu.c
> > index 0d9eb778794d92418b39f8535d94abde3566de43..9d274600e6a80bdfc435f6c6eff77c9dd71cb38c 100644
> > --- a/drivers/gpu/drm/sprd/sprd_dpu.c
> > +++ b/drivers/gpu/drm/sprd/sprd_dpu.c
> > @@ -3,6 +3,7 @@
> >   * Copyright (C) 2020 Unisoc Inc.
> >   */
> >  
> > +#include <linux/clk.h>
> >  #include <linux/component.h>
> >  #include <linux/delay.h>
> >  #include <linux/dma-buf.h>
> > @@ -794,6 +795,12 @@ static int sprd_dpu_context_init(struct sprd_dpu *dpu,
> >  	if (ctx->irq < 0)
> >  		return ctx->irq;
> >  
> > +	ctx->clk = devm_clk_get_optional_enabled(dev, "core");
> > +	if (IS_ERR(ctx->clk)) {
> > +		dev_err(dev, "failed to get DPU core clock\n");
> > +		return PTR_ERR(ctx->clk);
> > +	}
> > +
> >  	/* disable and clear interrupts before register dpu IRQ. */
> >  	writel(0x00, ctx->base + REG_DPU_INT_EN);
> >  	writel(0xff, ctx->base + REG_DPU_INT_CLR);
> > diff --git a/drivers/gpu/drm/sprd/sprd_dpu.h b/drivers/gpu/drm/sprd/sprd_dpu.h
> > index 157a78f24dc18b071602552ea9d005af66525263..d48b922de580a8a4bf07c4610c431d3321f7b810 100644
> > --- a/drivers/gpu/drm/sprd/sprd_dpu.h
> > +++ b/drivers/gpu/drm/sprd/sprd_dpu.h
> > @@ -44,6 +44,7 @@ enum {
> >   */
> >  struct dpu_context {
> >  	void __iomem *base;
> > +	struct clk *clk;
> >  	int irq;
> >  	u8 if_type;
> >  	struct videomode vm;
> > diff --git a/drivers/gpu/drm/sprd/sprd_dsi.c b/drivers/gpu/drm/sprd/sprd_dsi.c
> > index e01d1d28fe579644ec2e0c83ec9170269932adfe..2af4273a6c73185084290c9d14b8ac18914d514b 100644
> > --- a/drivers/gpu/drm/sprd/sprd_dsi.c
> > +++ b/drivers/gpu/drm/sprd/sprd_dsi.c
> > @@ -828,6 +828,8 @@ static void sprd_dsi_bridge_pre_enable(struct drm_bridge *bridge)
> >  	struct sprd_dsi *dsi = bridge_to_dsi(bridge);
> >  	struct dsi_context *ctx = &dsi->ctx;
> >  
> > +	clk_prepare_enable(ctx->clk);
> > +
> >  	if (ctx->enabled) {
> >  		drm_warn(dsi->drm, "dsi is initialized\n");
> >  		return;
> > @@ -875,6 +877,8 @@ static void sprd_dsi_bridge_post_disable(struct drm_bridge *bridge)
> >  	sprd_dphy_fini(ctx);
> >  	sprd_dsi_fini(ctx);
> >  
> > +	clk_disable_unprepare(ctx->clk);
> > +
> >  	ctx->enabled = false;
> >  }
> 
> I'm a bit confused. Why do you need to enable / disable that clock in
> pre_enable / post_disable, if you already enabled it at probe?

These are two different clocks. DPU uses devm_clk_get_optional_enabled,
while DSI uses devm_clk_get_optional and enables/disables it when
needed. Ideally both clocks should be disabled when not needed, but this
will be implemented later.

Best regards,
Otto Pflüger