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Date:   Mon, 7 Dec 2020 11:12:50 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
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3:32, Michael S. Tsirkin wrote:
> On Sat, Dec 05, 2020 at 08:59:55AM +0100, Enrico Weigelt, metux IT consult wrote:
>> On 04.12.20 04:35, Jason Wang wrote:
>>
>>>> --- a/drivers/gpio/Kconfig
>>>> +++ b/drivers/gpio/Kconfig
>>>> @@ -1615,6 +1615,15 @@ config GPIO_MOCKUP
>>>>         tools/testing/selftests/gpio/gpio-mockup.sh. Reference the
>>>> usage in
>>>>         it.
>>>>   +config GPIO_VIRTIO
>>>> +    tristate "VirtIO GPIO support"
>>>> +    depends on VIRTIO
>>>
>>> Let's use select, since there's no prompt for VIRTIO and it doesn't have
>>> any dependencies.
>> whoops, it's not that simple:
>>
>> make: Entering directory '/home/nekrad/src/apu2-dev/pkg/kernel.apu2.git'
>> make[1]: Entering directory
>> '/home/nekrad/src/dk/DistroKit/platform-x86_64/build-target/linux-5.8.9-build'
>>    GEN     Makefile
>> drivers/gpu/drm/Kconfig:74:error: recursive dependency detected!
>> drivers/gpu/drm/Kconfig:74:	symbol DRM_KMS_HELPER is selected by
>> DRM_VIRTIO_GPU
>> drivers/gpu/drm/virtio/Kconfig:2:	symbol DRM_VIRTIO_GPU depends on VIRTIO
>> drivers/virtio/Kconfig:2:	symbol VIRTIO is selected by GPIO_VIRTIO
>> drivers/gpio/Kconfig:1618:	symbol GPIO_VIRTIO depends on GPIOLIB
>> drivers/gpio/Kconfig:14:	symbol GPIOLIB is selected by I2C_MUX_LTC4306
>> drivers/i2c/muxes/Kconfig:47:	symbol I2C_MUX_LTC4306 depends on I2C
>> drivers/i2c/Kconfig:8:	symbol I2C is selected by FB_DDC
>> drivers/video/fbdev/Kconfig:63:	symbol FB_DDC depends on FB
>> drivers/video/fbdev/Kconfig:12:	symbol FB is selected by DRM_KMS_FB_HELPER
>> drivers/gpu/drm/Kconfig:80:	symbol DRM_KMS_FB_HELPER depends on
>> DRM_KMS_HELPER
>>
>> Seems that we can only depend on or select some symbol - we run into
>> huge trouble if thats mixed. Just changed DRM_VIRTIO_GPU to just select
>> VIRIO instead of depending on it, and now it works.
>>
>> I've posted another patch for fixing drivers/gpu/drm/virtio/Kconfig
>> to use 'select' instead of 'depends on'.
> 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.
>
> The text near it says:
>
> # SPDX-License-Identifier: GPL-2.0-only
> config VIRTIO
>          tristate
>          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.
>
> 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 ...


For testing like switching bus from pci to MMIO?


> And for virtio fs it was like this from the beginning.
>
> I am inclined to fix console and virtio fs to depend on VIRTIO:
> select is harder to use correctly ...
>
> Jason?


I think it works, but we need a prompt for VIRTIO otherwise there's no 
way to enable it.

Thanks


>
>
>> -- 
>> ---
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>> ---
>> Enrico Weigelt, metux IT consult
>> Free software and Linux embedded engineering
>> info@...ux.net -- +49-151-27565287

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