linux-kernel - Re: [PATCH] cdx: Fix missing GENERIC_MSI

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Message-ID: <96a17356-b233-4438-be79-25bf56696bc8@linaro.org>
Date: Fri, 18 Jul 2025 16:08:53 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: Nipun Gupta <nipun.gupta@....com>, Nikhil Agarwal
 <nikhil.agarwal@....com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] cdx: Fix missing GENERIC_MSI_IRQ on compile test

On 17/07/2025 22:40, Alex Williamson wrote:
> On Thu, 17 Jul 2025 13:33:58 -0600
> Alex Williamson <alex.williamson@...hat.com> wrote:
> 
>> On Wed, 16 Jul 2025 08:49:04 +0200
>> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
>>
>>> CDX_BUS driver uses msi_setup_device_data() which is selected by
>>> GENERIC_MSI_IRQ, thus compile testing without the latter failed:
>>>
>>>   /usr/bin/ld: drivers/cdx/cdx.o: in function `cdx_probe':
>>>   build/drivers/cdx/cdx.c:314: undefined reference to `msi_setup_device_data'
>>>
>>> Reported-by: Randy Dunlap <rdunlap@...radead.org>
>>> Closes: https://lore.kernel.org/all/b2c54a12-480c-448a-8b90-333cb03d9c14@infradead.org/
>>> Fixes: 7f81907b7e3f ("cdx: Enable compile testing")
>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>> ---
>>>  drivers/cdx/Kconfig | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/cdx/Kconfig b/drivers/cdx/Kconfig
>>> index 1f1e360507d7..3af41f51cf38 100644
>>> --- a/drivers/cdx/Kconfig
>>> +++ b/drivers/cdx/Kconfig
>>> @@ -8,6 +8,7 @@
>>>  config CDX_BUS
>>>  	bool "CDX Bus driver"
>>>  	depends on OF && ARM64 || COMPILE_TEST
>>> +	select GENERIC_MSI_IRQ
>>>  	help
>>>  	  Driver to enable Composable DMA Transfer(CDX) Bus. CDX bus
>>>  	  exposes Fabric devices which uses composable DMA IP to the  
>>
>> This looks incomplete to me.  The Makefile has:
>>
>> ifdef CONFIG_GENERIC_MSI_IRQ
>> obj-$(CONFIG_CDX_BUS) += cdx_msi.o
>> endif
>>
>> The call to msi_setup_device_data(), the conditional inclusion of
>> cdx_msi.o, and cdx_msi.c itself were added in 0e439ba38e61 ("cdx: add
>> MSI support for CDX bus").  That's the source of the issue, not the
>> Kconfig update to build under COMPILE_TEST, but also the Makefile
>> should be updated to statically include cdx_msi.o.  Thanks,
> 
> Also, we may not be philosophically aligned on this, but if CDX_BUS
> selects GENERIC_MSI_IRQ and CDX_CONTROLLER depends on CDX_BUS, then the
> select of the same under CDX_CONTROLLER becomes redundant.

I don't have a preference for that. I imagine that they use/depend on
MSI independently of each other. At least I could imagine such code.


> 
> Independent of that there are also some ifdefs in cdx_bus.h that would
> become invalid if the entire CDX_BUS depends on GENERIC_MSI_IRQ.  It

These ifdefs are for cdx_msi.c which looks like quite independent piece
of code from cdx.c.

> really kinda looks like CDX_BUS expects a use case that doesn't depend
> on GENERIC_MSI_IRQ and I wonder if the right answer isn't just:

Yes, I agree.

> 
> diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
> index 092306ca2541..3d50f8cd9c0b 100644
> --- a/drivers/cdx/cdx.c
> +++ b/drivers/cdx/cdx.c
> @@ -310,7 +310,7 @@ static int cdx_probe(struct device *dev)
>  	 * Setup MSI device data so that generic MSI alloc/free can
>  	 * be used by the device driver.
>  	 */
> -	if (cdx->msi_domain) {
> +	if (IS_ENABLED(CONFIG_GENERIC_MSI_IRQ) && cdx->msi_domain) {
>  		error = msi_setup_device_data(&cdx_dev->dev);
>  		if (error)
>  			return error;
> @@ -833,7 +833,7 @@ int cdx_device_add(struct cdx_dev_params *dev_params)
>  		     ((cdx->id << CDX_CONTROLLER_ID_SHIFT) | (cdx_dev->bus_num & CDX_BUS_NUM_MASK)),
>  		     cdx_dev->dev_num);
>  
> -	if (cdx->msi_domain) {
> +	if (IS_ENABLED(CONFIG_GENERIC_MSI_IRQ) && cdx->msi_domain) {
>  		cdx_dev->num_msi = dev_params->num_msi;
>  		dev_set_msi_domain(&cdx_dev->dev, cdx->msi_domain);
>  	}
> 
> Then I suppose vfio-cdx would also have the option to either
> select/depend on GENERIC_MSI_IRQ or perhaps get away with stubbing
> vfio_cdx_set_irqs_ioctl and vfio_cdx_irqs_cleanup and conditionally
> building intr.o, depending on if there's a use case without MSI.
> Thanks,

vfio/cdx/intr.c unconditionally calls cdx_enable_msi() and entire code
looks like relies on MSI. cdx_enable_msi() stub seems to be only for the
purpose of modular builds.

But these are just guesses...




Best regards,
Krzysztof