linux-kernel - Re: [RFC PATCH v1 2/2] usb: host: add xhci-exynos to support Exynos SOCs

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Date:   Mon, 5 Dec 2022 12:30:34 +0900
From:   Jung Daehwan <dh10.jung@...sung.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Colin Ian King <colin.i.king@...il.com>,
        Artur Bujdoso <artur.bujdoso@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Tomer Maimon <tmaimon77@...il.com>,
        "open list:USB SUBSYSTEM" <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/SAMSUNG S3C, S5P AND EXYNOS ARM ARCHITECTURES" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/SAMSUNG S3C, S5P AND EXYNOS ARM ARCHITECTURES" 
        <linux-samsung-soc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, sc.suh@...sung.com,
        taehyun.cho@...sung.com, jh0801.jung@...sung.com,
        eomji.oh@...sung.com
Subject: Re: [RFC PATCH v1 2/2] usb: host: add xhci-exynos to support Exynos
 SOCs

On Thu, Dec 01, 2022 at 09:06:55AM +0100, Greg Kroah-Hartman wrote:
> On Thu, Dec 01, 2022 at 11:13:31AM +0900, Daehwan Jung wrote:
> > This driver works with xhci platform driver. It needs to override
> > functions of xhci_plat_hc_driver. Wakelocks are used for sleep/wakeup
> > scenario of system.
> 
> So this means that no other platform xhci driver can be supported in the
> same system at the same time.
> 
> Which kind of makes sense as that's not anything a normal system would
> have, BUT it feels very odd.  This whole idea of "override the platform
> driver" feels fragile, why not make these just real platform drivers and
> have the xhci platform code be a library that the other ones can use?
> That way you have more control overall, right?
> 
> thanks,
> 
> greg k-h
> 

Currently It seems there are 2 ways to excute own function.
1. xhci_plat_priv
-> This is hard to use it if the driver invokes xhci platform driver from
dwc3_host_init(usb/dwc/host.c). I can't pass driver data during probe.
2. xhci_driver_overrides
-> This is only useful if I has own xhci driver.

That's why I wanted to extend overriding concept of xhci platform driver.
If some code is better to be directly in xhci platform driver than xhci-exynos,
I will modify it.

Best Regard,
Jung Daehwan