[lkml]   [2019]   [Dec]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 2/2] PCI: uniphier: Add checking whether PERST# is deasserted

On 06/12/19 2:28 pm, Kunihiko Hayashi wrote:
> Hi Kishon,
> On Fri, 6 Dec 2019 12:28:29 +0530 <> wrote:
>> Hi,
>> On 04/12/19 3:35 pm, Kunihiko Hayashi wrote:
>>> On Fri, 22 Nov 2019 20:53:16 +0900 <> wrote:
>>>>> Hello Lorenzo,
>>>> On Thu, 21 Nov 2019 16:47:05 +0000 <> wrote:
>>>>> On Fri, Nov 08, 2019 at 04:30:27PM +0900, Kunihiko Hayashi wrote:
>>>>>>> However, If I understand correctly, doesn't your solution only work some
>>>>>>> of the time? What happens if you boot both machines at the same time,
>>>>>>> and PERST# isn't asserted prior to the kernel booting?
>>>>>> I think it contains an annoying problem.
>>>>>> If PERST# isn't toggled prior to the kernel booting, PERST# remains asserted
>>>>>> and the RC driver can't access PCI bus.
>>>>>> As a result, this patch works and deasserts PERST# (and EP configuration will
>>>>>> be lost). So boot sequence needs to include deasserting PERST#.
>>>>> I am sorry but I have lost you. Can you explain to us why checking
>>>>> that PERST# is deasserted guarantees you that:
>>>>> - The EP has bootstrapped
>>>>> - It is safe not to toggle it again (and also skip
>>>>> uniphier_pcie_ltssm_enable())
>>>>> Please provide details of the HW configuration so that we understand
>>>>> what's actually supposed to happen and why this patch fixes the
>>>>> issue you are facing.
>>>> I tried to connect between the following boards, and do pci-epf-test:
>>>> - "RC board": UniPhier ld20 board that has DWC RC controller
>>>> - "EP board": UniPhier legacy board that has DWC EP controller
>>>> This EP has power-on-state configuration, but it's necessary to set
>>>> class ID, BAR sizes, etc. after starting up.
>>>> In case of that starting up RC board before EP board, the RC driver
>>>> can't establish link. So we need to boot EP board first.
>>>> At that point, I've considered why RC can't establish link,
>>> and found that the waitng time was too short.
>>>> - EP/RC: power on both boards
>>>> - RC: start up the kernel on RC board
>>>> - RC: wait for link up (long time enough)
>>>> - EP: start up the kernel on EP board
>>>> - EP: configurate pci-epf-test
>>>> When the endpoint configuration is done and the EP driver enables LTSSM,
>>> the RC driver will quit from waiting for link up.
>>>> Currently DWC RC driver calls dwc_pcie_wait_for_link(), however,
>>> the function tries to link up 10 times only, that is defined
>>> as LINK_WAIT_MAX_RETRIES in pcie-designware.h, it's too short
>>> to configurate the endpoint.
>>>> Now the patch to bypass PERST# is not necessary.
>>>> Instead for DWC RC drivers, I think that the number of retries
>>> should be changed according to the usage.
>>> And the same issue remains with other RC drivers.
>> If EP is configured using Linux, then PERST# cannot be used as it's difficult to boot linux and initialize EP within the specified time interval. Can't you prevent PERST from being propagated at all?
> Surely it might be difficult for RC to decide the time to wait for EP.
> Since RC almost toggles PERST# in boot time, I'd like to think about
> how to prevent from first PERST# at least.

It can be prevented in the HW (If that's possible). I modify the cable
connecting RC and EP to not propagate PERST#.


 \ /
  Last update: 2019-12-06 10:01    [W:0.072 / U:3.972 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site