linux-kernel - Re: [PATCH v2 2/2] PCI: designware-ep: Fix the access to DBI/iATU registers before enabling controller

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Date:   Wed, 5 Jan 2022 19:43:04 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Kishon Vijay Abraham I <kishon@...com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Xiaowei Bao <xiaowei.bao@....com>,
        Om Prakash Singh <omp@...dia.com>,
        Vidya Sagar <vidyas@...dia.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] PCI: designware-ep: Fix the access to DBI/iATU
 registers before enabling controller

Hi Kishon, Lorenzo,

Thank you and sorry for late reply.

On 2021/12/06 20:23, Lorenzo Pieralisi wrote:
> On Fri, Dec 03, 2021 at 10:36:00AM +0530, Kishon Vijay Abraham I wrote:
>> Hi Kunihiko,
>>
>> On 01/09/21 10:46 am, Kunihiko Hayashi wrote:
>>> The driver using core_init_notifier, e.g. pcie-tegra194.c, runs
> according
>>> to the following sequence:
>>>
>>>      probe()
>>>          dw_pcie_ep_init()
>>>
>>>      bind()
>>>          dw_pcie_ep_start()
>>>              enable_irq()
>>>
>>>      (interrupt occurred)
>>>      handler()
>>>          [enable controller]
>>>          dw_pcie_ep_init_complete()
>>>          dw_pcie_ep_init_notify()
>>>
>>> After receiving an interrupt from RC, the handler enables the
> controller
>>> and the controller registers can be accessed.
>>> So accessing the registers should do in dw_pcie_ep_init_complete().
>>>
>>> Currently dw_pcie_ep_init() has functions dw_iatu_detect() and
>>> dw_pcie_ep_find_capability() that include accesses to DWC registers.
>>> As a result, accessing the registers before enabling the controller,
>>> the access will fail.
>>>
>>> The function dw_pcie_ep_init() shouldn't have any access to DWC
> registers
>>> if the controller is enabled after calling bind(). This moves access
> codes
>>> to DBI/iATU registers and depending variables from dw_pcie_ep_init()
> to
>>> dw_pcie_ep_init_complete().
>>
>> Ideally pci_epc_create() should be the last step by the controller
>> driver before handing the control to the core EPC framework. Since
>> after this step the EPC framework can start invoking the epc_ops.
>>
>> Here more stuff is being added to dw_pcie_ep_init_complete() which is
>> required for epc_ops and this could result in aborts for platforms
>> which does not add core_init_notifier.
> 
> This patch needs rework, I will mark the series as "Changes requested".

I understand that relocation of dwc register accesses isn't appropriate,
but I couldn't think of any other rework to dwc, and I confirmed
pcie-qcom-ep driver using core_init_notifier.

In pcie-qcom-ep driver, probe() enables clock and deasserts reset first,
and when PERST# interrupt arrives, the handler enables clock and deasserts
reset again. So, dw_pcie_ep_init() can access DBI registers.

In pcie-tegra194 driver, I think the issue will be solved if probe() also
handles clock and reset control. However, the driver has other register
access between core_clk, core_apb_rst, and core_rst controls.
I think that it's appropriate to leave this fix to the developer at this
point.

As this patch series, I'll resend 1/2 patch only and expect pcie-tegra194
driver to be fixed.

Thank you,

---
Best Regards
Kunihiko Hayashi