linux-kernel - Re: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary

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Message-ID: <cfec2252044b208efef6ffd14a50f334528ceec3.camel@wdc.com>
Date: Sun, 25 May 2025 02:36:42 +0000
From: Wilfred Mallawa <wilfred.mallawa@....com>
To: "kw@...ux.com" <kw@...ux.com>, "bhelgaas@...gle.com"
	<bhelgaas@...gle.com>, "manivannan.sadhasivam@...aro.org"
	<manivannan.sadhasivam@...aro.org>, "lpieralisi@...nel.org"
	<lpieralisi@...nel.org>
CC: "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"cassel@...nel.org" <cassel@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "lukas@...ner.de" <lukas@...ner.de>
Subject: Re: [PATCH 1/2] PCI: Save and restore root port config space in
 pcibios_reset_secondary_bus()

On Sun, 2025-05-25 at 00:23 +0530, Manivannan Sadhasivam wrote:
> host_bridge::reset_slot() is supposed to reset the PCI root
> port/slot. Once
> that happens, the config space content would be lost. This was
> reported by
> Niklas on the dw-rockchip based platform where the MPS setting of the
> root
> port was lost after the host_bridge::reset_slot() callback. Hence,
> save the
> config space before calling the host_bridge::reset_slot() callback
> and
> restore it afterwards.
> 
> While at it, make sure that the callback is only called for root
> ports by
> checking if the bridge is behind the root bus.
> 
> Fixes: d5c1e1c25b37 ("PCI/ERR: Add support for resetting the slots in
> a platform specific way")
> Reported-by: Niklas Cassel <cassel@...nel.org>
> Closes: https://lore.kernel.org/linux-pci/aC9OrPAfpzB_A4K2@ryzen
> Suggested-by: Lukas Wunner <lukas@...ner.de>
> Signed-off-by: Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/pci.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 4d396bbab4a8..6d6e9ce2bbcc 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4985,10 +4985,19 @@ void __weak
> pcibios_reset_secondary_bus(struct pci_dev *dev)
>  	struct pci_host_bridge *host = pci_find_host_bridge(dev-
> >bus);
>  	int ret;
>  
> -	if (host->reset_slot) {
> +	if (pci_is_root_bus(dev->bus) && host->reset_slot) {
> +		/*
> +		 * Save the config space of the root port before
> doing the
> +		 * reset, since the state could be lost. The device
> state
> +		 * should've been saved by the caller.
> +		 */
> +		pci_save_state(dev);
>  		ret = host->reset_slot(host, dev);
>  		if (ret)
>  			pci_err(dev, "failed to reset slot: %d\n",
> ret);
> +		else
> +			/* Now restore it on success */
> +			pci_restore_state(dev);
>  
>  		return;
>  	}
Reviewed-by: Wilfred Mallawa <wilfred.mallawa@....com>