Re: [PATCH 09/10] NTB: epf: Fix doorbell bitmask handling in db_read/db_clear

On 2/24/26 6:34 AM, Koichiro Den wrote:
> The EPF driver currently stores the incoming doorbell as a vector number
> (irq_no + 1) in db_val and db_clear() clears all bits unconditionally.
> This breaks db_read()/db_clear() semantics when multiple doorbells are
> used.
> 
> Store doorbells as a bitmask (BIT_ULL(vector)) and make
> db_clear(db_bits) clear only the specified bits. Use atomic64 operations
> as db_val is updated from interrupt context.
> 
> Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
> Signed-off-by: Koichiro Den <[email protected]>
> ---
>  drivers/ntb/hw/epf/ntb_hw_epf.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> index 00956ab2fbf5..0018adc35f16 100644
> --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> @@ -6,6 +6,7 @@
>   * Author: Kishon Vijay Abraham I <[email protected]>
>   */
>  
> +#include <linux/atomic.h>
>  #include <linux/delay.h>
>  #include <linux/module.h>
>  #include <linux/pci.h>
> @@ -102,7 +103,7 @@ struct ntb_epf_dev {
>  	unsigned int self_spad;
>  	unsigned int peer_spad;
>  
> -	int db_val;
> +	atomic64_t db_val;
>  	u64 db_valid_mask;
>  };
>  
> @@ -331,15 +332,16 @@ static irqreturn_t ntb_epf_vec_isr(int irq, void *dev)
>  	int irq_no;
>  
>  	irq_no = irq - pci_irq_vector(ndev->ntb.pdev, 0);
> -	ndev->db_val = irq_no + 1;
>  
>  	if (irq_no == 0) {
>  		ntb_link_event(&ndev->ntb);
>  	} else if (irq_no == 1) {
>  		dev_warn_ratelimited(ndev->dev,
>  				     "Unexpected irq_no 1 received. Treat it as DB#0.\n");
> +		atomic64_or(BIT_ULL(0), &ndev->db_val);
>  		ntb_db_event(&ndev->ntb, 0);
>  	} else {
> +		atomic64_or(BIT_ULL(irq_no - 2), &ndev->db_val);

Again here the bits probably can use a define or enum instead of magic numbers.

DJ

>  		ntb_db_event(&ndev->ntb, irq_no - 2);
>  	}
>  
> @@ -524,7 +526,7 @@ static u64 ntb_epf_db_read(struct ntb_dev *ntb)
>  {
>  	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
>  
> -	return ndev->db_val;
> +	return atomic64_read(&ndev->db_val);
>  }
>  
>  static int ntb_epf_db_clear_mask(struct ntb_dev *ntb, u64 db_bits)
> @@ -536,7 +538,7 @@ static int ntb_epf_db_clear(struct ntb_dev *ntb, u64 db_bits)
>  {
>  	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
>  
> -	ndev->db_val = 0;
> +	atomic64_and(~db_bits, &ndev->db_val);
>  
>  	return 0;
>  }