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 21:16:31 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Kishon Vijay Abraham I <kishon@...com>,
        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

On Wed, Jan 05, 2022 at 07:43:04PM +0900, Kunihiko Hayashi wrote:
> 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.
> 

Yes, only since dw_pcie_ep_init() carries out the DBI accesses, we have enabled
clocks and PHY. Moving the DBI accesses to init_complete() removes the need of
enabling the resources redundantly.

Thanks,
Mani

> 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