linux-kernel - Re: [PATCH v2 2/2] drivers: gpio: add virtio-gpio guest driver

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Date:   Mon, 7 Dec 2020 11:16:16 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        linux-kernel@...r.kernel.org, corbet@....net,
        linus.walleij@...aro.org, bgolaszewski@...libre.com,
        linux-doc@...r.kernel.org, linux-gpio@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-riscv@...ts.infradead.org, stefanha@...hat.com,
        msuchanek@...e.de
Subject: Re: [PATCH v2 2/2] drivers: gpio: add virtio-gpio guest driver


On 2020/12/6 上午4:05, Enrico Weigelt, metux IT consult wrote:
> On 05.12.20 20:32, Michael S. Tsirkin wrote:
>
> Hi,
>
>> It seems a bit of a mess, at this point I'm not entirely sure when
>> should drivers select VIRTIO and when depend on it.
> if VIRTIO just enables something that could be seen as library
> functions, then select should be right, IMHO.
>
>> The text near it says:
>>
>> # SPDX-License-Identifier: GPL-2.0-only
>> config VIRTIO
>>          tristate
> oh, wait, doesn't have an menu text, so we can't even explicitly enable
> it (not shown in menu) - only implicitly. Which means that some other
> option must select it, in order to become availe at all, and in order
> to make others depending on it becoming available.
>
> IMHO, therefore select is the correct approach.
>
>
>>          help
>>            This option is selected by any driver which implements the virtio
>>            bus, such as CONFIG_VIRTIO_PCI, CONFIG_VIRTIO_MMIO, CONFIG_RPMSG
>>            or CONFIG_S390_GUEST.
>>
>> Which seems clear enough and would indicate drivers for devices *behind*
>> the bus should not select VIRTIO and thus presumably should "depend on" it.
>> This is violated in virtio console and virtio fs drivers.
> See above: NAK. because it can't even be enabled directly (by the user).
> If it wasn't meant otherwise, we'd have to add an menu text.
>
>> For console it says:
>>
>> commit 9f30eb29c514589e16f2999ea070598583d1f6ec
>> Author: Michal Suchanek <msuchanek@...e.de>
>> Date:   Mon Aug 31 18:58:50 2020 +0200
>>
>>      char: virtio: Select VIRTIO from VIRTIO_CONSOLE.
>>      
>>      Make it possible to have virtio console built-in when
>>      other virtio drivers are modular.
>>      
>>      Signed-off-by: Michal Suchanek <msuchanek@...e.de>
>>      Reviewed-by: Amit Shah <amit@...nel.org>
>>      Link: https://lore.kernel.org/r/20200831165850.26163-1-msuchanek@suse.de
>>      Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>
>> which seems kind of bogus - why do we care about allowing a builtin
>> virtio console driver if the pci virtio bus driver is a module?
>> There won't be any devices on the bus to attach to ...
> When using other transports ?
> In my current project, eg. I'm using mmio - my kernel has pci completely
> disabled.
>
>> I am inclined to fix console and virtio fs to depend on VIRTIO:
>> select is harder to use correctly ...
> I don't thinkt that would be good - instead everybody should just select
> VIRTIO, never depend on it (maybe depend on VIRTIO_MENU instead)


I'm fine with either. Though I prefer to use select but it looks to me 
adding a prompt and use enable would be easier.

Thanks


>
>
> --mtx
>