linux-kernel - Re: [PATCH V4 XDMA 2/2] dmaengine: xilinx: xdma: Add user logic interrupt support

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Date:   Tue, 27 Sep 2022 11:14:44 -0700
From:   Lizhi Hou <lizhi.hou@....com>
To:     Martin Tůma <tumic@...see.org>,
        <vkoul@...nel.org>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <trix@...hat.com>
CC:     <max.zhen@....com>, <sonal.santan@....com>, <larry.liu@....com>,
        <brian.xu@....com>
Subject: Re: [PATCH V4 XDMA 2/2] dmaengine: xilinx: xdma: Add user logic
 interrupt support


On 9/27/22 10:54, Martin Tůma wrote:
> On 27. 09. 22 19:18, Lizhi Hou wrote:
>>
>> On 9/27/22 09:46, Martin Tůma wrote:
>>> On 27. 09. 22 18:28, Lizhi Hou wrote:
>>>
>>>> Okay, I got the point. How about changing request/remove APIs to 
>>>> enable/disable APIs as below
>>>>
>>>>       xdma_enable_user_irq(struct platform_device *pdev, u32 
>>>> user_irq_index, u32 *irq)
>>>>
>>>>              user_irq_index: user logic interrupt wire index. (XDMA 
>>>> driver determines how system IRQs are mapped to DMA channels and 
>>>> user logic wires)
>>>>
>>>>              irq: IRQ number returned for registering interrupt 
>>>> handler (request_irq()) or passing to existing platform driver.
>>>>
>>>>      xdma_disable_user_irq(struct platform_device *pdev, u32 
>>>> user_irq_index)
>>>>
>>>> Does this make sense to you?
>>>>
>>>
>>> I think even the "irq" parameter in the enable function is surplus 
>>> as the parent driver (the driver of the actual PCIe card) knows* 
>>> what PCI irq he has to allocate without XDMA providing the number.
>>>
>>> xdma_enable_user_irq(struct platform_device *pdev, u32 user_irq_index);
>>> xdma_disable_user_irq(struct platform_device *pdev, u32 
>>> user_irq_index);
>>>
>>> should be all that is needed.
>>>
>>> M.
>>>
>>> * something like:
>>> pci_irq_vector((pdev), PCI_BAR_ID) + NUM_C2H_CHANNELS + 
>>> NUM_H2C_CHANNELS
>>> can be used from the PCIe driver
>>
>> How does parent driver know the first few vectors will be assigned to 
>> DMA channel?  Parent diver should not assume the first 
>> (NUM_C2H_CHANNELS+NUM_H2C_CHANNELS) are for DMA channel.
>>
>> Parent driver passes the system IRQ range  to XDMA driver, and only 
>> XDMA driver knows what IRQs are used by DMA channel and what IRQs are 
>> mapped to user logic wires. I would keep the "u32 *irq" argument.
>>
>
> The parent driver knows how much DMA channels it wants/allocates. If 
> it is possible to allocate different IRQs than the first 
> NUM_C2H_CHANNELS + NUM_H2C_CHANNELS to the XDMA IP core, than that 
> parameter may be needed, but I haven't seen such HW. Moreover, every 
> parent driver author should IMHO know how the channel and user IRQs 
> are mapped in their specific HW configuration so this info can be 
> "hard-wired" in the parent driver, but I'm fine with it when the irq 
> parameter is kept anyway. All I really need is that the enable/disable 
> logic is split from the irq allocate/register logic so I can use the 
> other platform drivers.
>
> M.

Thanks Mark, all your comments are very helpful. And glad to know you 
are fine with irq parameter. The IRQ binding is set by xdma driver ( 
xdma_set_vector_reg() ). That means xdma driver is able to map any 
system IRQ to dma channel or user logic. That is why I prefer to keep 
irq parameter. Just a FYI.

Lizhi