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

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Message-ID: <f633b0f3-9fdb-8beb-7edf-7967c7c0c3d5@linaro.org>
Date:   Fri, 2 Dec 2022 13:23:56 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daehwan Jung <dh10.jung@...sung.com>
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>,
        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 02/12/2022 13:22, Mathias Nyman wrote:
> On 1.12.2022 11.01, Arnd Bergmann wrote:
>> On Thu, Dec 1, 2022, at 09:06, 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?
> 
> Agree that overriding the generic platform driver xhci_hc_platform_driver
> from this exynos driver is odd.
> 
> But I don't understand how this works.
> Where are the hcds created and added when this xhci-exonys driver binds to
> the device? all this driver does in probe is the overriding?
> 
> Am I missing something here?

Because it is not a driver for Exynos... it's a driver for wakelocks for
their specific Android use-cases which the manufacturer ships for their
Android devices. Due to Google GKI, they try to squeeze into upstream.
But this is huge misconception what should go to upstream and Samsung
does not want to keep discussing. They just send random patches and
disappear...

Best regards,
Krzysztof