linux-kernel - Re: [PATCH 1/3] PCI: Add support in pci_walk

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Date:   Mon, 20 Sep 2021 09:56:07 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        <lokeshvutla@...com>
Subject: Re: [PATCH 1/3] PCI: Add support in pci_walk_bus() to invoke callback matching RID

On Mon, 20 Sep 2021 07:41:31 +0100,
Kishon Vijay Abraham I <kishon@...com> wrote:
> 
> Add two arguments to pci_walk_bus() [requestorID and mask], and add
> support in pci_walk_bus() to invoke the *callback* only for devices
> whose RequestorID after applying *mask* matches with *requestorID*
> passed as argument.
> 
> This is done in preparation for calculating the total number of
> interrupt vectors that has to be supported by a specific GIC ITS device ID,
> specifically when "msi-map-mask" is populated in device tree.
> 
> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/pci/bus.c   | 13 +++++++++----
>  include/linux/pci.h |  7 +++++--
>  2 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 3cef835b375f..e381e639ceaa 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -358,10 +358,12 @@ void pci_bus_add_devices(const struct pci_bus *bus)
>  }
>  EXPORT_SYMBOL(pci_bus_add_devices);
>  
> -/** pci_walk_bus - walk devices on/under bus, calling callback.
> +/** __pci_walk_bus - walk devices on/under bus matching requestor ID, calling callback.
>   *  @top      bus whose devices should be walked
>   *  @cb       callback to be called for each device found
>   *  @userdata arbitrary pointer to be passed to callback.
> + *  @rid      Requestor ID that has to be matched for the callback to be invoked
> + *  @mask     Mask that has to be applied to pci_dev_id(), before compating it with @rid
>   *
>   *  Walk the given bus, including any bridged devices
>   *  on buses under this bus.  Call the provided callback
> @@ -371,8 +373,8 @@ EXPORT_SYMBOL(pci_bus_add_devices);
>   *  other than 0, we break out.
>   *
>   */
> -void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> -		  void *userdata)
> +void __pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> +		    void *userdata, u32 rid, u32 mask)
>  {
>  	struct pci_dev *dev;
>  	struct pci_bus *bus;
> @@ -399,13 +401,16 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>  		} else
>  			next = dev->bus_list.next;
>  
> +		if (mask != 0xffff && ((pci_dev_id(dev) & mask) != rid))

Why the check for the mask? I also wonder whether the mask should apply
to the rid as well:

		if ((pci_dev_id(dev) & mask) != (rid & mask))

> +			continue;
> +
>  		retval = cb(dev, userdata);
>  		if (retval)
>  			break;
>  	}
>  	up_read(&pci_bus_sem);
>  }
> -EXPORT_SYMBOL_GPL(pci_walk_bus);
> +EXPORT_SYMBOL_GPL(__pci_walk_bus);
>  
>  struct pci_bus *pci_bus_get(struct pci_bus *bus)
>  {
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index cd8aa6fce204..8500fec56e50 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1473,14 +1473,17 @@ const struct pci_device_id *pci_match_id(const struct pci_device_id *ids,
>  int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
>  		    int pass);
>  
> -void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> -		  void *userdata);
> +void __pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> +		    void *userdata, u32 rid, u32 mask);
>  int pci_cfg_space_size(struct pci_dev *dev);
>  unsigned char pci_bus_max_busnr(struct pci_bus *bus);
>  void pci_setup_bridge(struct pci_bus *bus);
>  resource_size_t pcibios_window_alignment(struct pci_bus *bus,
>  					 unsigned long type);
>  
> +#define pci_walk_bus(top, cb, userdata) \
> +	 __pci_walk_bus((top), (cb), (userdata), 0x0, 0xffff)

Please keep this close to the helper it replaces. I also really
dislike the use of this raw 0xffff. Don't we already have a named
constant that represents the mask for a RID?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.