linux-kernel - Re: [PATCH v3 18/25] PCI: pciehp: Use RESPONSE_IS_PCI

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Date:   Thu, 21 Oct 2021 20:52:53 +0530
From:   Naveen Naidu <naveennaidu479@...il.com>
To:     bhelgaas@...gle.com
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        skhan@...uxfoundation.org, Lukas Wunner <lukas@...ner.de>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Amey Narkhede <ameynarkhede03@...il.com>
Subject: Re: [PATCH v3 18/25] PCI: pciehp: Use RESPONSE_IS_PCI_ERROR() to
 check read from hardware

On 21/10, Naveen Naidu wrote:
> An MMIO read from a PCI device that doesn't exist or doesn't respond
> causes a PCI error.  There's no real data to return to satisfy the
> CPU read, so most hardware fabricates ~0 data.
> 
> Use RESPONSE_IS_PCI_ERROR() to check the response we get when we read
> data from hardware.
> 
> This helps unify PCI error response checking and make error checks
> consistent and easier to find.
> 
> Compile tested only.
> 
> Signed-off-by: Naveen Naidu <naveennaidu479@...il.com>
> ---
>  drivers/pci/hotplug/pciehp_hpc.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 3024d7e85e6a..f472f83f6cce 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -89,7 +89,7 @@ static int pcie_poll_cmd(struct controller *ctrl, int timeout)
>  
>  	do {
>  		pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
> -		if (slot_status == (u16) ~0) {
> +		if (RESPONSE_IS_PCI_ERROR(slot_status)) {
>  			ctrl_info(ctrl, "%s: no response from device\n",
>  				  __func__);
>  			return 0;
> @@ -165,7 +165,7 @@ static void pcie_do_write_cmd(struct controller *ctrl, u16 cmd,
>  	pcie_wait_cmd(ctrl);
>  
>  	pcie_capability_read_word(pdev, PCI_EXP_SLTCTL, &slot_ctrl);
> -	if (slot_ctrl == (u16) ~0) {
> +	if (RESPONSE_IS_PCI_ERROR(slot_ctrl)) {
>  		ctrl_info(ctrl, "%s: no response from device\n", __func__);
>  		goto out;
>  	}
> @@ -236,7 +236,7 @@ int pciehp_check_link_active(struct controller *ctrl)
>  	int ret;
>  
>  	ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
> -	if (ret == PCIBIOS_DEVICE_NOT_FOUND || lnk_status == (u16)~0)
> +	if (ret == PCIBIOS_DEVICE_NOT_FOUND || RESPONSE_IS_PCI_ERROR(lnk_status))
>  		return -ENODEV;
>  
>  	ret = !!(lnk_status & PCI_EXP_LNKSTA_DLLLA);
> @@ -443,7 +443,7 @@ int pciehp_card_present(struct controller *ctrl)
>  	int ret;
>  
>  	ret = pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
> -	if (ret == PCIBIOS_DEVICE_NOT_FOUND || slot_status == (u16)~0)
> +	if (ret == PCIBIOS_DEVICE_NOT_FOUND || RESPONSE_IS_PCI_ERROR(slot_status))
>  		return -ENODEV;
>  
>  	return !!(slot_status & PCI_EXP_SLTSTA_PDS);
> @@ -621,7 +621,7 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
>  
>  read_status:
>  	pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &status);
> -	if (status == (u16) ~0) {
> +	if (RESPONSE_IS_PCI_ERROR(status)) {
>  		ctrl_info(ctrl, "%s: no response from device\n", __func__);
>  		if (parent)
>  			pm_runtime_put(parent);
> -- 
> 2.25.1
> 

Lukas, I have not added your Acked-by tag from the v1 [1] of the patch 
series, since the RESPONSE_IS_PCI_ERROR macro definition slightly 
changed. I hope this was the right thing to do.

[1]: https://lore.kernel.org/linux-pci/20211011194740.GA14357@wunner.de/

Also, regarding your comments from v1 patch series [1] about re-naming
the RESPONSE_IS_PCI_ERROR to RESPONSE_IS_PCI_TIMEOUT. We could indeed 
change the change to RESPONSE_IS_PCI_TIMEOUT for pciehp, but then 
I'm afraid that picehp would be the odd one out. I mean, since in all 
the other places we are using RESPONE_IS_PCI_TIMEOUT to see if any 
error occured while reading from a device.

RESPONSE_IS_PCI_ERROR stills gives an idea to the readers that some PCI
error occured. It was my understanding that timeout is also a kind of
PCI error (I might be horribly wrong here, given my very less experience
with PCI subsystem) so it would be okay to use RESPONSE_IS_PCI_ERROR
here.

If that is not the case please let me know. But I am not sure what to
do here? If RESPONSE_IS_PCI_ERROR does not fit here, should the right
option would be to revert/remove this patch from the series?

Thanks,
Naveen