linux-kernel - Re: [PATCH] usb: dwc3: Always deassert xilinx resets

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Message-ID: <20260113235334.t6cx2y2zrj436wtb@synopsys.com>
Date: Tue, 13 Jan 2026 23:53:51 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Sean Anderson <sean.anderson@...ux.dev>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>,
        "open list:DESIGNWARE USB3 DRD IP DRIVER" <linux-usb@...r.kernel.org>,
        "Frager, Neal" <neal.frager@....com>,
        "Simek,  Michal" <michal.simek@....com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/ZYNQ ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: dwc3: Always deassert xilinx resets

On Tue, Jan 13, 2026, Sean Anderson wrote:
> On 1/12/26 19:49, Thinh Nguyen wrote:
> > On Fri, Jan 09, 2026, Sean Anderson wrote:
> >> On 1/9/26 01:01, Pandey, Radhey Shyam wrote:
> >> > [AMD Official Use Only - AMD Internal Distribution Only]
> >> > 
> >> >> -----Original Message-----
> >> >> From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
> >> >> Sent: Friday, January 9, 2026 6:19 AM
> >> >> To: Sean Anderson <sean.anderson@...ux.dev>
> >> >> Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>; open list:DESIGNWARE
> >> >> USB3 DRD IP DRIVER <linux-usb@...r.kernel.org>; Frager, Neal
> >> >> <neal.frager@....com>; Simek, Michal <michal.simek@....com>; open list
> >> >> <linux-kernel@...r.kernel.org>; moderated list:ARM/ZYNQ ARCHITECTURE
> >> >> <linux-arm-kernel@...ts.infradead.org>; Philipp Zabel <p.zabel@...gutronix.de>;
> >> >> Pandey, Radhey Shyam <radhey.shyam.pandey@....com>; Greg Kroah-Hartman
> >> >> <gregkh@...uxfoundation.org>
> >> >> Subject: Re: [PATCH] usb: dwc3: Always deassert xilinx resets
> >> >>
> >> >> On Tue, Jan 06, 2026, Sean Anderson wrote:
> >> >> > If we don't have a usb3 phy we don't need to assert the core resets.
> >> >> > Deassert them even if we didn't assert them to support booting when
> >> >> > the bootloader never released the core from reset.
> >> > Is it a customized bootloader ? i.e it assert reset but don't deassert.
> >> 
> >> No. Most peripheral resets are asserted on PoR. So if the bootloader
> >> doesn't deassert them then Linux has to.
> >> 
> >> My goal is to make init_serdes() in psu_init_gpl.c optional and do all
> >> serdes initialization in the phy driver (and in the consumer drivers). I
> >> have this working for DP/PCIe. I'm working on SATA, and I don't think
> >> USB/SGMII need much special. This gives the following advantages:
> >> 
> >> - On some boards (mine) the reference clocks may not be configured in
> >>   SPL/FSBL. So ILL calibration will fail (and take a long time to do so)
> >>   unless we defer initialization to U-Boot/Linux where the phy driver
> >>   can request the clocks.
> >> - If PCIe/SATA are not used in U-Boot, ILL calibration can be deferred
> >>   until Linux when it can be done it parallel with other initialization.
> >> - We will have flexibility to switch between different serdes
> >>   configurations at runtime. For example, this could allow the
> >>   bootloader to fixup the devicetree to support PCIe and SATA M.2
> >>   drives, depending on what the user has plugged in.
> >> 
> >> > I think ideally core /APB reset should be done independent on
> >> > MAC 2.0/3.0 configuration.
> >> 
> >> I agree, but I think the existing code does this optimization to reduce
> >> boot time when the bootloader has already initialized USB. I have
> >> preserved that in this patch.
> >> 
> > 
> > I think all this info is useful. Can we include it in the change log?
> 
> OK, how about:
> 
> I am working on moving serdes initialization to the phy (and consumer)
> drivers to improve flexibility and boot times (depending on
> configuration). Currently, core resets are released in the bootloader by
> init_serdes() in psu_init_gpl.c. In order to remove init_serdes, we
> need to handle the case where the bootloader never released the core
> resets. If we don't have a usb3 phy we don't need to assert the core
> resets, but deassert them anyway to handle this case.
> 
> We could assert all resets every boot, but I believe the existing
> procedure is an optimization to reduce boot time when the bootloader has
> already initialized USB. So this patch preserves the separate code
> paths.

Sounds good to me! Typically we write it in imperative mood, but it's
just minor nit. I care more about the motivation behind these changes.

Radhey can comment if there's doubt.

Otherwise, you can add this in v2:

Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>

Thanks,
Thinh