linux-kernel - Re: [PATCH 3/3] usb: renesas_usbhs: Reorder clock handling and power management in probe

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Message-ID: <87zfh6yoly.wl-kuninori.morimoto.gx@renesas.com>
Date: Fri, 28 Mar 2025 00:40:09 +0000
From: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To: Prabhakar <prabhakar.csengg@...il.com>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	linux-usb@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Biju Das <biju.das.jz@...renesas.com>,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH 3/3] usb: renesas_usbhs: Reorder clock handling and power management in probe

Hi Prabhakark

Thank you for the patch

> Reorder the initialization sequence in `usbhs_probe()` to enable runtime
> PM before accessing registers, preventing potential crashes due to
> uninitialized clocks.
> 
> Currently, in the probe path, registers are accessed before enabling the
> clocks, leading to a synchronous external abort on the RZ/V2H SoC.
> The problematic call flow is as follows:
> 
>     usbhs_probe()
>         usbhs_sys_clock_ctrl()
>             usbhs_bset()
>                 usbhs_write()
>                     iowrite16()  <-- Register access before enabling clocks

This patch itself is not so bad idea, but basically, we should not assume
the power/clock was enabled since kernel boot.
In this driver, register access happen only during power enable <->  power
disable (except your issue case), and this is good idea. So, the strange
is usbhs_sys_clock_ctrl() call in usbhs_probe() (without power enable) I
guess.

According to the comment, it is just caring boot loader, and
usbhs_sys_clock_ctrl() itself will be called when usbhsc_power_ctrl() was
called anyway. And more, if my understanding was correct, Renesas clock
driver will stop all unused devices clock/power after boot.
So maybe we can just remove strange usbhs_sys_clock_ctrl() from usbhs_probe() ?

Thank you for your help !!

Best regards
---
Kuninori Morimoto