linux-kernel - Re: [PATCH v12 18/25] CXL/AER: Introduce aer_cxl_vh.c in AER driver for forwarding CXL errors

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Message-ID: <6dfabc9f-4244-4f8f-9bff-434b5758cd4a@amd.com>
Date: Fri, 3 Oct 2025 15:12:30 -0500
From: "Cheatham, Benjamin" <benjamin.cheatham@....com>
To: Terry Bowman <terry.bowman@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<dave@...olabs.net>, <jonathan.cameron@...wei.com>, <dave.jiang@...el.com>,
	<alison.schofield@...el.com>, <dan.j.williams@...el.com>,
	<bhelgaas@...gle.com>, <shiju.jose@...wei.com>, <ming.li@...omail.com>,
	<Smita.KoralahalliChannabasappa@....com>, <rrichter@....com>,
	<dan.carpenter@...aro.org>, <PradeepVineshReddy.Kodamati@....com>,
	<lukas@...ner.de>, <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	<linux-cxl@...r.kernel.org>, <alucerop@....com>, <ira.weiny@...el.com>
Subject: Re: [PATCH v12 18/25] CXL/AER: Introduce aer_cxl_vh.c in AER driver
 for forwarding CXL errors

[snip]

> +
> +void cxl_forward_error(struct pci_dev *pdev, struct aer_err_info *info)
> +{
> +	struct cxl_proto_err_work_data wd = (struct cxl_proto_err_work_data) {
> +		.severity = info->severity,
> +		.pdev = pdev
> +	};
> +
> +	guard(rwsem_write)(&cxl_proto_err_kfifo.rw_sema);
> +
> +	if (!cxl_proto_err_kfifo.work) {
> +		dev_warn_once(&pdev->dev, "CXL driver is not registered for kfifo");

I don't think this is a very useful error message to an end user. Maybe something like
"CXL driver is not registered for error forwarding" instead?

> +		return;
> +	}
> +
> +	if (!kfifo_put(&cxl_proto_err_kfifo.fifo, wd)) {
> +		dev_err_ratelimited(&pdev->dev, "CXL kfifo overflow\n");

Less sure about this one, since it's an actual error with the kfifo. May want to mention
it's the CXL AER kfifo just in case another kfifo comes along in the CXL driver.

> +		return;
> +	}
> +
> +	schedule_work(cxl_proto_err_kfifo.work);
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_forward_error, "CXL");
> +
> +void cxl_register_proto_err_work(struct work_struct *work)
> +{
> +	guard(rwsem_write)(&cxl_proto_err_kfifo.rw_sema);
> +	cxl_proto_err_kfifo.work = work;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_register_proto_err_work, "CXL");
> +
> +void cxl_unregister_proto_err_work(void)
> +{
> +	guard(rwsem_write)(&cxl_proto_err_kfifo.rw_sema);
> +	cxl_proto_err_kfifo.work = NULL;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_unregister_proto_err_work, "CXL");
> +
> +int cxl_proto_err_kfifo_get(struct cxl_proto_err_work_data *wd)
> +{
> +	guard(rwsem_read)(&cxl_proto_err_kfifo.rw_sema);
> +	return kfifo_get(&cxl_proto_err_kfifo.fifo, wd);
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_proto_err_kfifo_get, "CXL");
> diff --git a/include/linux/aer.h b/include/linux/aer.h
> index 2ef820563996..6b2c87d1b5b6 100644
> --- a/include/linux/aer.h
> +++ b/include/linux/aer.h
> @@ -10,6 +10,7 @@
>  
>  #include <linux/errno.h>
>  #include <linux/types.h>
> +#include <linux/workqueue_types.h>
>  
>  #define AER_NONFATAL			0
>  #define AER_FATAL			1
> @@ -53,6 +54,16 @@ struct aer_capability_regs {
>  	u16 uncor_err_source;
>  };
>  
> +/**
> + * struct cxl_proto_err_work_data - Error information used in CXL error handling
> + * @severity: AER severity
> + * @pdev: PCI device detecting the error
> + */
> +struct cxl_proto_err_work_data {
> +	int severity;
> +	struct pci_dev *pdev;
> +};
> +
>  #if defined(CONFIG_PCIEAER)
>  int pci_aer_clear_nonfatal_status(struct pci_dev *dev);
>  int pcie_aer_is_native(struct pci_dev *dev);
> @@ -68,8 +79,14 @@ static inline void pci_aer_unmask_internal_errors(struct pci_dev *dev) { }
>  
>  #ifdef CONFIG_CXL_RAS
>  bool cxl_error_is_native(struct pci_dev *dev);
> +int cxl_proto_err_kfifo_get(struct cxl_proto_err_work_data *wd);
> +void cxl_register_proto_err_work(struct work_struct *work);
> +void cxl_unregister_proto_err_work(void);
>  #else
>  static inline bool cxl_error_is_native(struct pci_dev *dev) { return false; }
> +static inline int cxl_proto_err_kfifo_get(struct cxl_proto_err_work_data *wd) { return 0; }
> +static inline void cxl_register_proto_err_work(struct work_struct *work) { }
> +static inline void cxl_unregister_proto_err_work(void) { }
>  #endif
>  
>  void pci_print_aer(struct pci_dev *dev, int aer_severity,

Feels weird to add all this plumbing and then it goes unused. Assuming it's not a heavy lift,
I would like to see at the CXL driver register stubs at least.