Re: [PATCH v2 0/8] PCI: Enable Power and configure the QPS615 PCIe switch

[Krishna Chaitanya Chundru <quic_krichai@quicinc.com>]

On 8/3/2024 4:26 PM, Dmitry Baryshkov wrote:
> On Sat, Aug 03, 2024 at 08:52:46AM GMT, Krishna chaitanya chundru wrote:
>> QPS615 is the PCIe switch which has one upstream and three downstream
>> ports. One of the downstream ports is used as endpoint device of Ethernet
>> MAC. Other two downstream ports are supposed to connect to external
>> device. One Host can connect to QPS615 by upstream port.
>>
>> QPS615 switch power is controlled by the GPIO's. After powering on
>> the switch will immediately participate in the link training. if the
>> host is also ready by that time PCIe link will established.
>>
>> The QPS615 needs to configured certain parameters like de-emphasis,
>> disable unused port etc before link is established.
>>
>> The device tree properties are parsed per node under pci-pci bridge in the
>> devicetree. Each node has unique bdf value in the reg property, driver
>> uses this bdf to differentiate ports, as there are certain i2c writes to
>> select particulat port.
>>   
>> As the controller starts link training before the probe of pwrctl driver,
>> the PCIe link may come up before configuring the switch itself.
>> To avoid this introduce two functions in pci_ops to start_link() &
>> stop_link() which will disable the link training if the PCIe link is
>> not up yet.
>>
>> Now PCI pwrctl device is the child of the pci-pcie bridge, if we want
>> to enable the suspend resume for pwrctl device there may be issues
>> since pci bridge will try to access some registers in the config which
>> may cause timeouts or Un clocked access as the power can be removed in
>> the suspend of pwrctl driver.
>>
>> To solve this make PCIe controller as parent to the pci pwr ctrl driver
>> and create devlink between host bridge and pci pwrctl driver so that
>> pci pwrctl driver will go suspend only after all the PCIe devices went
>> to suspend.
>>
>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
>> ---
>> Changes in V1:
>> - Fix the code as per the comments given.
> 
> This is not a proper changelog entry. It doesn't allow reviewers to
> understand what actually happened. Could you please list your actual
> changes in a reply and also include them in a changelog if there is a
> need for v3.
> 
ack
- Krishna Chaitanya.
>> - Removed D3cold D0 sequence in suspend resume for now as it needs
>>    seperate discussion.
>> - change to dt approach for configuring the switch instead of request_firmware() approach
>> - Link to v1: https://lore.kernel.org/linux-pci/20240626-qps615-v1-4-2ade7bd91e02@quicinc.com/T/
>> ---
>>
>