linux-kernel - Re: [PATCH v2 3/3] dwc: PCI: intel: Intel PCIe RC controller driver

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Date:   Tue, 27 Aug 2019 16:47:32 +0800
From:   Dilip Kota <eswara.kota@...ux.intel.com>
To:     "Chuan Hua, Lei" <chuanhua.lei@...ux.intel.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     andriy.shevchenko@...el.com, cheol.yong.kim@...el.com,
        devicetree@...r.kernel.org, gustavo.pimentel@...opsys.com,
        hch@...radead.org, jingoohan1@...il.com,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        qi-ming.wu@...el.com
Subject: Re: [PATCH v2 3/3] dwc: PCI: intel: Intel PCIe RC controller driver

Hi Martin,

On 8/27/2019 11:09 AM, Chuan Hua, Lei wrote:
[...]
>
>
>> now I am wondering:
>> - if we don't have to disable the interrupt line (once it is enabled),
>> why can't we enable all of these interrupts at initialization time
>> (instead of doing it on-demand)?
> Good point! we even can remote map_irq patch, directly call
>
> of_irq_parse_and_map_pci as other drivers do.

Irrespective of disabling, imo interrupts(A/B/C/D) should be enabled 
when they are requested; which happens during map_irq() call.

>> - if the interrupts do have to be disabled again (that is what I
>> assumed so far) then where is this supposed to happen? (my solution
>> for this was to implement a simple interrupt controller within the
>> PCIe driver which only supports enable/disable. disclaimer: I didn't
>> ask the PCI or interrupt maintainers for feedback on this yet)
>>
>> [...]
>
> We can implement one interrupt controller, but personally, it has too
>
> much overhead. If we follow this way, almost all modules of all old
>
> lantiq SoCs can implement one interrupt controller. Maybe you can check
>
> with PCI maintainer for their comments.
>
[...]
>>> This is needed. In the old driver, we fixed this by fixup. The original
>>> comment as follows,
>>>
>>> /*
>>>    * The root complex has a hardwired class of 
>>> PCI_CLASS_NETWORK_OTHER or
>>>    * PCI_CLASS_BRIDGE_HOST, when it is operating as a root complex this
>>>    * needs to be switched to * PCI_CLASS_BRIDGE_PCI
>>>    */
>> that would be a good comment to add if you really need it
>> can you please look at dw_pcie_setup_rc (from 
>> pcie-designware-host.c), it does:
>>    /* Enable write permission for the DBI read-only register */
>>    dw_pcie_dbi_ro_wr_en(pci);
>>    /* Program correct class for RC */
>>    dw_pcie_wr_own_conf(pp, PCI_CLASS_DEVICE, 2, PCI_CLASS_BRIDGE_PCI);
>>    /* Better disable write permission right after the update */
>>    dw_pcie_dbi_ro_wr_dis(pci);
>>
>> so my understanding is that there is a functional requirement to set
>> the class to PCI_CLASS_BRIDGE_PCI
>> however, that requirement is already covered by pcie-designware-host.c
> I will task Dilip to check if we can use dwc one.
dw_pcie_setup_rc () cannot be called here because, it is not doing 
PCI_CLASS_BRIDGE_PCI set alone, it is configuring many other things.

[...]


Regards,

Dilip