linux-kernel - Re: [PATCH 2/2] media: pci: mgb4: remove bogus 'select' statements

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Message-Id: <7acec62a-6b5c-4635-b486-ceadee279f35@app.fastmail.com>
Date:   Fri, 27 Oct 2023 15:29:34 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Lizhi Hou" <lizhi.hou@....com>, "Arnd Bergmann" <arnd@...nel.org>,
        "Martin Tuma" <martin.tuma@...iteqautomotive.com>,
        "Mauro Carvalho Chehab" <mchehab@...nel.org>,
        "Hans Verkuil" <hverkuil-cisco@...all.nl>,
        dmaengine@...r.kernel.org, "Brian Xu" <brian.xu@....com>,
        "Raj Kumar Rampelli" <raj.kumar.rampelli@....com>,
        "Vinod Koul" <vkoul@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] media: pci: mgb4: remove bogus 'select' statements

On Tue, Oct 24, 2023, at 18:18, Lizhi Hou wrote:
> On 10/24/23 06:27, Arnd Bergmann wrote:
>> On Mon, Oct 23, 2023, at 18:05, Arnd Bergmann wrote:
>>
>> aarch64-linux-ld: drivers/media/pci/mgb4/mgb4_core.o: in function `init_i2c': mgb4_core.c:(.text+0x3ec): undefined reference to `xdma_get_user_irq'
>> aarch64-linux-ld: mgb4_core.c:(.text+0x404): undefined reference to `xdma_enable_user_irq'
>>
>> I couldn't easily figure out what a 'user_irq' is here,
>> but I wonder if this is the expected way to use the DMA engine
>> layer. Maybe this should have been a nested irqchip instead,
>> or it should be encoded in the DMA request specifier?
>
> Hi Arnd,
>
> Here is a brief description of 'user_irq' and 'xdma_enable_user_irq'
>
> The XDMA subsystem is used in conjunction with the PCIe IP block. Please 
> see https://lwn.net/Articles/911496/ for the overall information.
>
> XDMA can forward PCIe msi-x interrupt to/from user logic hardware (e.g. 
> Digiteq device) which is connected to its user irq pin.  And XDMA has a 
> register to enable/disabe interrupt forwarding for a specific user irq pin.
>
> 'xdma_enable_user_irq' and 'xdma_disable_user_irq' are provided for 
> hardware driver which is designed to use XDMA to enable/disable its 
> interrupt. And based on the previous discussion with Mark, Digiteq 
> device does not use its own register to enable/disable interrupt but 
> relies on XDMA.  Please see 
> https://lore.kernel.org/lkml/daccee4a-ac3c-bfc1-4876-24e6ecf5bcf1@gpxsee.org/

Ok, in this case, I would suggest using 'depends on XILINX_XDMA'
instead of the 'select' statement. I'll send a v2.

     Arnd