linux-kernel - Re: [RFC PATCH v2 10/27] NTB: core: Add .get_pci_epc() to ntb_dev

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Message-ID: <f6jo2z4dnk23dun7g7d6d4ul2rw7do2cugb7jtq4tfb4vixzsw@lmpl5p4kqxc6>
Date: Tue, 2 Dec 2025 15:32:24 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Dave Jiang <dave.jiang@...el.com>
Cc: ntb@...ts.linux.dev, linux-pci@...r.kernel.org, 
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, Frank.Li@....com, mani@...nel.org, 
	kwilczynski@...nel.org, kishon@...nel.org, bhelgaas@...gle.com, corbet@....net, 
	vkoul@...nel.org, jdmason@...zu.us, allenbh@...il.com, Basavaraj.Natikar@....com, 
	Shyam-sundar.S-k@....com, kurt.schwemmer@...rosemi.com, logang@...tatee.com, 
	jingoohan1@...il.com, lpieralisi@...nel.org, robh@...nel.org, jbrunet@...libre.com, 
	fancer.lancer@...il.com, arnd@...db.de, pstanner@...hat.com, 
	elfring@...rs.sourceforge.net
Subject: Re: [RFC PATCH v2 10/27] NTB: core: Add .get_pci_epc() to ntb_dev_ops

On Mon, Dec 01, 2025 at 02:08:14PM -0700, Dave Jiang wrote:
> 
> 
> On 11/29/25 9:03 AM, Koichiro Den wrote:
> > Add an optional get_pci_epc() callback to retrieve the underlying
> > pci_epc device associated with the NTB implementation.
> > 
> > Signed-off-by: Koichiro Den <den@...inux.co.jp>
> > ---
> >  drivers/ntb/hw/epf/ntb_hw_epf.c | 11 +----------
> >  include/linux/ntb.h             | 21 +++++++++++++++++++++
> >  2 files changed, 22 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> > index a3ec411bfe49..d55ce6b0fad4 100644
> > --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> > +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> > @@ -9,6 +9,7 @@
> >  #include <linux/delay.h>
> >  #include <linux/module.h>
> >  #include <linux/pci.h>
> > +#include <linux/pci-epf.h>
> >  #include <linux/slab.h>
> >  #include <linux/ntb.h>
> >  
> > @@ -49,16 +50,6 @@
> >  
> >  #define NTB_EPF_COMMAND_TIMEOUT	1000 /* 1 Sec */
> >  
> > -enum pci_barno {
> > -	NO_BAR = -1,
> > -	BAR_0,
> > -	BAR_1,
> > -	BAR_2,
> > -	BAR_3,
> > -	BAR_4,
> > -	BAR_5,
> > -};
> > -
> >  enum epf_ntb_bar {
> >  	BAR_CONFIG,
> >  	BAR_PEER_SPAD,
> > diff --git a/include/linux/ntb.h b/include/linux/ntb.h
> > index d7ce5d2e60d0..04dc9a4d6b85 100644
> > --- a/include/linux/ntb.h
> > +++ b/include/linux/ntb.h
> > @@ -64,6 +64,7 @@ struct ntb_client;
> >  struct ntb_dev;
> >  struct ntb_msi;
> >  struct pci_dev;
> > +struct pci_epc;
> >  
> >  /**
> >   * enum ntb_topo - NTB connection topology
> > @@ -256,6 +257,7 @@ static inline int ntb_ctx_ops_is_valid(const struct ntb_ctx_ops *ops)
> >   * @msg_clear_mask:	See ntb_msg_clear_mask().
> >   * @msg_read:		See ntb_msg_read().
> >   * @peer_msg_write:	See ntb_peer_msg_write().
> > + * @get_pci_epc:	See ntb_get_pci_epc().
> >   */
> >  struct ntb_dev_ops {
> >  	int (*port_number)(struct ntb_dev *ntb);
> > @@ -331,6 +333,7 @@ struct ntb_dev_ops {
> >  	int (*msg_clear_mask)(struct ntb_dev *ntb, u64 mask_bits);
> >  	u32 (*msg_read)(struct ntb_dev *ntb, int *pidx, int midx);
> >  	int (*peer_msg_write)(struct ntb_dev *ntb, int pidx, int midx, u32 msg);
> > +	struct pci_epc *(*get_pci_epc)(struct ntb_dev *ntb);
> 
> Seems very specific call to this particular hardware instead of something generic for the NTB dev ops. Maybe it should be something like get_private_data() or something like that?

Thank you for the suggestion.

I also felt that it's too specific, but I couldn't come up with a clean
generic interface at the time, so I left it in this form.

.get_private_data() might indeed be better. In the callback doc comment we
could describe it as "may be used to obtain a backing PCI controller
pointer"?

-Koichiro

> 
> DJ
> 
> 
> >  };
> >  
> >  static inline int ntb_dev_ops_is_valid(const struct ntb_dev_ops *ops)
> > @@ -393,6 +396,9 @@ static inline int ntb_dev_ops_is_valid(const struct ntb_dev_ops *ops)
> >  		/* !ops->msg_clear_mask == !ops->msg_count	&& */
> >  		!ops->msg_read == !ops->msg_count		&&
> >  		!ops->peer_msg_write == !ops->msg_count		&&
> > +
> > +		/* Miscellaneous optional callbacks */
> > +		/* ops->get_pci_epc			&& */
> >  		1;
> >  }
> >  
> > @@ -1567,6 +1573,21 @@ static inline int ntb_peer_msg_write(struct ntb_dev *ntb, int pidx, int midx,
> >  	return ntb->ops->peer_msg_write(ntb, pidx, midx, msg);
> >  }
> >  
> > +/**
> > + * ntb_get_pci_epc() - get backing PCI endpoint controller if possible.
> > + * @ntb:	NTB device context.
> > + *
> > + * Get the backing PCI endpoint controller representation.
> > + *
> > + * Return: A pointer to the pci_epc instance if available. or %NULL if not.
> > + */
> > +static inline struct pci_epc __maybe_unused *ntb_get_pci_epc(struct ntb_dev *ntb)
> > +{
> > +	if (!ntb->ops->get_pci_epc)
> > +		return NULL;
> > +	return ntb->ops->get_pci_epc(ntb);
> > +}
> > +
> >  /**
> >   * ntb_peer_resource_idx() - get a resource index for a given peer idx
> >   * @ntb:	NTB device context.
>