linux-kernel - Re: [PATCH] PCI: keystone: Don't enable BAR0 if link is not detected

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Message-ID: <025ec85f-78be-4b0f-9c5b-f59087610c67@ti.com>
Date:   Wed, 18 Oct 2023 16:19:40 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     Serge Semin <fancer.lancer@...il.com>
CC:     Bjorn Helgaas <helgaas@...nel.org>, <lpieralisi@...nel.org>,
        <robh@...nel.org>, <kw@...ux.com>, <bhelgaas@...gle.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <r-gunasekaran@...com>,
        <srk@...com>, <s-vadapalli@...com>
Subject: Re: [PATCH] PCI: keystone: Don't enable BAR0 if link is not detected

On 18/10/23 16:12, Serge Semin wrote:
> On Tue, Oct 17, 2023 at 09:44:51AM +0530, Siddharth Vadapalli wrote:
>> Hello,
>>
>> On 17/10/23 02:59, Serge Semin wrote:
>>> Hi Siddharth
>>>
>>
>> ...
>>

...

> 
> Are you really sure that it's 4.90a? Here is what my DW PCIe RC
> _v4.90_ HW databook says about the BARs:
> 
> "Base Address Registers (Offset: 0x10-x14) The Synopsys core does not
> implement the optional BARs for the RC product. This is based on the
> assumption that the RC host probably has registers on some other
> internal bus and has knowledge and setup access to these registers
> already."
> 
> What you cited resides in the _v5.x_ databooks. It makes my thinking
> that in your case the IP-core isn't of 4.90a version.

I reviewed the function ks_pcie_v3_65_add_bus() and it appears clear to me now
that it is applicable only to 3.65a versions. The IP-core however is 4.90a. I
have posted the v2 patch at:
https://lore.kernel.org/r/20231018075038.2740534-1-s-vadapalli@ti.com/

Also, as pointed out by Ravi on the v2 patch's thread at:
https://lore.kernel.org/r/c546f8e9-f6ba-41b8-7dff-4a7921b6705f@ti.com/
the culprit turned out to be:
6ab15b5e7057 (PCI: dwc: keystone: Convert .scan_bus() callback to use add_bus)
which in the process of converting the .scan_bus() callback to .add_bus(), namely:
ks_pcie_v3_65_scan_bus() -> ks_pcie_v3_65_add_bus()
It added the .add_bus() method within "struct pci_ops ks_pcie_ops" which is
actually shared with the 4.90a controller as well. So an "is_am6" check should
have also been added to make it no-op for NON-3.65a controllers.

I will be posting the v3 patch implementing the above fix if there is no further
feedback on the v2 patch from others.

-- 
Regards,
Siddharth.