linux-kernel - Re: [PATCH v2 3/3] usb: renesas_usbhs: Reorder clock handling and power management in probe

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Message-ID: <CAMuHMdWXid=9NXUULSA-vedZyjvDKJWt2KX8_Y=arMOp_-gFRQ@mail.gmail.com>
Date: Tue, 8 Apr 2025 17:42:55 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Cc: Prabhakar <prabhakar.csengg@...il.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>, 
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, Biju Das <biju.das.jz@...renesas.com>, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v2 3/3] usb: renesas_usbhs: Reorder clock handling and
 power management in probe

Hi Shimoda-san,

On Tue, 8 Apr 2025 at 12:40, Yoshihiro Shimoda
<yoshihiro.shimoda.uh@...esas.com> wrote:
> > From: Prabhakar, Sent: Monday, April 7, 2025 7:50 PM
> >
> > Reorder the initialization sequence in `usbhs_probe()` to enable runtime
> > PM before accessing registers, preventing potential crashes due to
> > uninitialized clocks.
>
> Just for a record. I don't know why, but the issue didn't occur on the original code
> with my environment (R-Car H3). But, anyway, I understood that we need this patch for RZ/V2H.

On R-Car Gen3 and later, the firmware must trap the external abort,
as usually no crash happens, but register reads return zero when
the module clock is turned off.  I am wondering why RZ/V2H behaves
differently than R-Car Gen3?

On R-Car Gen2, you do get an external abort when accessing hardware
registers while the module's clock is turned off.  Has anyone tested
usbhs on R-Car Gen2 recently?

> ----- I added some debug printk -----
> <snip>
> [    3.193400] usbhs_probe:706
> [    3.196204] usbhs_probe:710
> [    3.199012] usbhs_probe:715
> [    3.201808] usbhs_probe:720
> [    3.204605] usbhs_read: reg = 0

Hmm, did it read back sensible data?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds