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

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Message-ID: <ee561743-d4bc-0aa4-ded7-bfa6bd3a509b@linux.intel.com>
Date:   Thu, 29 Aug 2019 10:54:31 +0800
From:   "Chuan Hua, Lei" <chuanhua.lei@...ux.intel.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     eswara.kota@...ux.intel.com, 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, kishon@...com
Subject: Re: [PATCH v2 3/3] dwc: PCI: intel: Intel PCIe RC controller driver


On 8/29/2019 3:36 AM, Martin Blumenstingl wrote:
> On Wed, Aug 28, 2019 at 5:35 AM Chuan Hua, Lei
> <chuanhua.lei@...ux.intel.com> wrote:
> [...]
>>>>>>>> +static int intel_pcie_ep_rst_init(struct intel_pcie_port *lpp)
>>>>>>>> +{
>>>>>>>> +    struct device *dev = lpp->pci->dev;
>>>>>>>> +    int ret = 0;
>>>>>>>> +
>>>>>>>> +    lpp->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
>>>>>>>> +    if (IS_ERR(lpp->reset_gpio)) {
>>>>>>>> +            ret = PTR_ERR(lpp->reset_gpio);
>>>>>>>> +            if (ret != -EPROBE_DEFER)
>>>>>>>> +                    dev_err(dev, "failed to request PCIe GPIO: %d\n", ret);
>>>>>>>> +            return ret;
>>>>>>>> +    }
>>>>>>>> +    /* Make initial reset last for 100ms */
>>>>>>>> +    msleep(100);
>>>>>>> why is there lpp->rst_interval when you hardcode 100ms here?
>>>>>> There are different purpose. rst_interval is purely for asserted reset
>>>>>> pulse.
>>>>>>
>>>>>> Here 100ms is to make sure the initial state keeps at least 100ms, then we
>>>>>> can reset.
>>>>> my interpretation is that it totally depends on the board design or
>>>>> the bootloader setup.
>>>> Partially, you are right. However, we should not add some dependency
>>>> here from
>>>> bootloader and board. rst_interval is just to make sure the pulse (low
>>>> active or high active)
>>>> lasts the specified the time.
>>> +Cc Kishon
>>>
>>> he recently added support for a GPIO reset line to the
>>> pcie-cadence-host.c [0] and I believe he's also maintaining
>>> pci-keystone.c which are both using a 100uS delay (instead of 100ms).
>>> I don't know the PCIe spec so maybe Kishon can comment on the values
>>> that should be used according to the spec.
>>> if there's then a reason why values other than the ones from the spec
>>> are needed then there should be a comment explaining why different
>>> values are needed (what problem does it solve).
>> spec doesn't guide this part. It is a board or SoC specific setting.
>> 100us also should work. spec only requirs reset duration should last
>> 100ms. The idea is that before reset assert and deassert, make sure the
>> default deassert status keeps some time. We take this value from
>> hardware suggestion long time back. We can reduce this value to 100us,
>> but we need to test on the board.
> OK. I don't know how other PCI controller drivers manage this. if the
> PCI maintainers are happy with this then I am as well
> maybe it's worth changing the comment to indicate that this delay was
> suggested by the hardware team (so it's clear that this is not coming
> from the PCI spec)
Dilip will change to 100us delay and run the test. I also need to run 
some tests for old boards(XRX350/550/PRX300) to confirm this has no 
impact on function.
> [...]
>>>>>>>> +static void __intel_pcie_remove(struct intel_pcie_port *lpp)
>>>>>>>> +{
>>>>>>>> +    pcie_rc_cfg_wr_mask(lpp, PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER,
>>>>>>>> +                        0, PCI_COMMAND);
>>>>>>> I expect logic like this to be part of the PCI subsystem in Linux.
>>>>>>> why is this needed?
>>>>>>>
>>>>>>> [...]
>>>>>> bind/unbind case we use this. For extreme cases, we use unbind and bind
>>>>>> to reset
>>>>>> PCI instead of rebooting.
>>>>> OK, but this does not seem Intel/Lantiq specific at all
>>>>> why isn't this managed by either pcie-designware-host.c or the generic
>>>>> PCI/PCIe subsystem in Linux?
>>>> I doubt if other RC driver will support bind/unbind. We do have this
>>>> requirement due to power management from WiFi devices.
>>> pcie-designware-host.c will gain .remove() support in Linux 5.4
>>> I don't understand how .remove() and then .probe() again is different
>>> from .unbind() followed by a .bind()
>> Good. If this is the case, bind/unbind eventually goes to probe/remove,
>> so we can remove this.
> OK. as far as I understand you need to call dw_pcie_host_deinit from
> the .remove() callback (which is missing in this version)
> (I'm using drivers/pci/controller/dwc/pcie-tegra194.c as an example,
> this driver is in linux-next and thus will appear in Linux 5.4)
Thanks for your information. We should adapt this in next version.
>
>
> Martin