linux-kernel - Re: [PATCH 1/2] PCI: rzg3s-host: Use pci_generic_config

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Message-ID: <ce0d29be-bdc5-415d-b6c0-00bd76d9919b@tuxon.dev>
Date: Mon, 8 Dec 2025 17:18:42 +0200
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
 bhelgaas@...gle.com, lpieralisi@...nel.org, kwilczynski@...nel.org,
 mani@...nel.org, robh@...nel.org
Cc: linux-pci@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
 Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [PATCH 1/2] PCI: rzg3s-host: Use pci_generic_config_write() for
 the root bus

Hi, Krishna,

On 12/6/25 03:29, Krishna Chaitanya Chundru wrote:
> 
> On 12/5/2025 4:54 PM, Claudiu wrote:
>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>
>> The Renesas RZ/G3S host controller allows writing to read-only PCIe
>> configuration registers when the RZG3S_PCI_PERM_CFG_HWINIT_EN bit is set in
>> the RZG3S_PCI_PERM register. However, callers of struct pci_ops::write
>> expect the semantics defined by the PCIe specification, meaning that writes
>> to read-only registers must not be allowed.
>>
>> The previous custom struct pci_ops::write implementation for the root bus
>> temporarily enabled write access before calling pci_generic_config_write().
>> This breaks the expected semantics.
>>
>> Remove the custom implementation and simply use pci_generic_config_write().
>>
>> Along with this change, the updates of the PCI_PRIMARY_BUS,
>> PCI_SECONDARY_BUS, and PCI_SUBORDINATE_BUS registers were moved so that
>> they no longer depends on the RZG3S_PCI_PERM_CFG_HWINIT_EN bit in the
>> RZG3S_PCI_PERM_CFG register, since these registers are R/W.
>>
> Don't you need fixes tag and back port to stable kernels, this patch looks
> like a bug fix.

I consider it was not a functional fix. The driver was just accepted for
v6.19 and though it will be included before the pull request is issued. Due
to this I haven't added it. If any, I'm adding the tag here.

Fixes: 7ef502fb35b2 ("PCI: Add Renesas RZ/G3S host controller driver")

Thank you,
Claudiu