linux-kernel - Re: [PATCH v4 03/11] drm/bridge: cdns-dsi: Fix Phy _init() and

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Date: Wed, 26 Jun 2024 19:00:39 +0530
From: Aradhya Bhatia <a-bhatia1@...com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil
 Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman
	<jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard
	<mripard@...nel.org>, Jyri Sarha <jyri.sarha@....fi>,
        Thomas Zimmermann
	<tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Daniel Vetter
	<daniel@...ll.ch>
CC: DRI Development List <dri-devel@...ts.freedesktop.org>,
        Linux Kernel List
	<linux-kernel@...r.kernel.org>,
        Dominik Haller <d.haller@...tec.de>, Sam
 Ravnborg <sam@...nborg.org>,
        Thierry Reding <treding@...dia.com>,
        Kieran
 Bingham <kieran.bingham+renesas@...asonboard.com>,
        Nishanth Menon
	<nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Praneeth Bajjuri
	<praneeth@...com>, Udit Kumar <u-kumar1@...com>,
        Devarsh Thakkar
	<devarsht@...com>,
        Jayesh Choudhary <j-choudhary@...com>, Jai Luthra
	<j-luthra@...com>
Subject: Re: [PATCH v4 03/11] drm/bridge: cdns-dsi: Fix Phy _init() and
 _exit()

Hi Tomi,

Thanks for reviewing the patches!

On 26/06/24 15:55, Tomi Valkeinen wrote:
> Hi,
> 
> On 22/06/2024 14:09, Aradhya Bhatia wrote:
>> Initialize the Phy during the cdns-dsi _resume(), and de-initialize it
>> during the _suspend().
>>
>> Also power-off the Phy from bridge_disable.
>>
>> Fixes: fced5a364dee ("drm/bridge: cdns: Convert to phy framework")
>> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
>> ---
>>   drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
>> b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
>> index 5159c3f0853e..d89c32bae2b9 100644
>> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
>> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
>> @@ -672,6 +672,10 @@ static void cdns_dsi_bridge_disable(struct
>> drm_bridge *bridge)
>>       if (dsi->platform_ops && dsi->platform_ops->disable)
>>           dsi->platform_ops->disable(dsi);
>>   +    phy_power_off(dsi->dphy);
>> +    dsi->link_initialized = false;
>> +    dsi->phy_initialized = false;
>> +
>>       pm_runtime_put(dsi->base.dev);
>>   }
>>   @@ -698,7 +702,6 @@ static void cdns_dsi_hs_init(struct cdns_dsi *dsi)
>>              DPHY_CMN_PDN | DPHY_PLL_PDN,
>>              dsi->regs + MCTL_DPHY_CFG0);
>>   -    phy_init(dsi->dphy);
>>       phy_set_mode(dsi->dphy, PHY_MODE_MIPI_DPHY);
>>       phy_configure(dsi->dphy, &output->phy_opts);
>>       phy_power_on(dsi->dphy);
>> @@ -1120,6 +1123,8 @@ static int __maybe_unused cdns_dsi_resume(struct
>> device *dev)
>>       clk_prepare_enable(dsi->dsi_p_clk);
>>       clk_prepare_enable(dsi->dsi_sys_clk);
>>   +    phy_init(dsi->dphy);
>> +
>>       return 0;
>>   }
>>   @@ -1127,10 +1132,11 @@ static int __maybe_unused
>> cdns_dsi_suspend(struct device *dev)
>>   {
>>       struct cdns_dsi *dsi = dev_get_drvdata(dev);
>>   +    phy_exit(dsi->dphy);
>> +
>>       clk_disable_unprepare(dsi->dsi_sys_clk);
>>       clk_disable_unprepare(dsi->dsi_p_clk);
>>       reset_control_assert(dsi->dsi_p_rst);
>> -    dsi->link_initialized = false;
>>       return 0;
>>   }
>>   
> 
> So with this patch, phy_init/exit will be called in the resume/suspend
> functions. That looks fine.
> 
> But the phy_power_on/phy_power_off looks odd to me. Here you add
> phy_power_off() to cdns_dsi_bridge_disable(), which sounds fine. But
> phy_power_on() is called in cdns_dsi_hs_init(), and that is called in
> cdns_dsi_bridge_enable() (which sounds fine), but also in
> cdns_dsi_bridge_pre_enable().
> 
> So doesn't that mean cdns_dsi_hs_init() call in cdns_dsi_bridge_enable()
> is extra, as it effectively does nothing (it exists right away if
> dsi->phy_initialized == true)?

That's right. When cdns_dsi_hs_init() is called from
cdns_dsi_bridge_enable(), it is simply expected to return since
phy_initialized is true.

I am not aware about the exact reasoning behind this, but this gets
addressed when I convert the _bridge_enable() to _bridge_pre_enable()
and drop the older _bridge_pre_enable() entirely.


Regards
Aradhya