linux-kernel - Re: [RFC 1/2] PCI-Express Non-Transparent Bridge Support

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Message-ID: <20120715235548.GC7551@jonmason-lab>
Date:	Sun, 15 Jul 2012 16:55:48 -0700
From:	Jon Mason <jon.mason@...el.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-pci@...r.kernel.org, Dave Jiang <dave.jiang@...el.com>
Subject: Re: [RFC 1/2] PCI-Express Non-Transparent Bridge Support

On Sat, Jul 14, 2012 at 10:10:15AM -0700, Greg KH wrote:
> On Fri, Jul 13, 2012 at 02:44:59PM -0700, Jon Mason wrote:
> > +static int max_num_cbs = 2;
> > +module_param(max_num_cbs, uint, 0644);
> > +MODULE_PARM_DESC(max_num_cbs, "Maximum number of NTB transport connections");
> > +
> > +static bool no_msix;
> > +module_param(no_msix, bool, 0644);
> > +MODULE_PARM_DESC(no_msix, "Do not allow MSI-X interrupts to be selected");
> 
> How would a user, or a distro, know to set these options?  Why are they
> even options at all?

Good question.  There is actually a potential benefit to disabling MSI-X.  The NTB device on one of our platforms only has 3 MSI-X vectors.  In the current driver design, that would limit them to 3 client/virtual devices.  However, there are 15bits in the ISR that can be used for the same purpose.  So, if you disable MSI-X, you can have 15 instead of 3.  

> 
> 
> > +struct ntb_device {
> > +	struct pci_dev *pdev;
> > +	struct msix_entry *msix_entries;
> > +	void __iomem *reg_base;
> > +	struct ntb_mw mw[NTB_NUM_MW];
> > +	struct {
> > +		unsigned int max_spads;
> > +		unsigned int max_db_bits;
> > +		unsigned int msix_cnt;
> > +	} limits;
> > +	struct {
> > +		void __iomem *pdb;
> > +		void __iomem *pdb_mask;
> > +		void __iomem *sdb;
> > +		void __iomem *sbar2_xlat;
> > +		void __iomem *sbar4_xlat;
> > +		void __iomem *spad_write;
> > +		void __iomem *spad_read;
> > +		void __iomem *lnk_cntl;
> > +		void __iomem *lnk_stat;
> > +		void __iomem *spci_cmd;
> > +	} reg_ofs;
> > +	void *ntb_transport;
> > +	void (*event_cb)(void *handle, unsigned int event);
> 
> Shouldn't the event be an enum?

No, that would be too smart.

> 
> > +	struct ntb_db_cb *db_cb;
> > +	unsigned char hw_type;
> > +	unsigned char conn_type;
> > +	unsigned char dev_type;
> > +	unsigned char num_msix;
> > +	unsigned char bits_per_vector;
> > +	unsigned char max_cbs;
> > +	unsigned char link_status;
> > +	struct delayed_work hb_timer;
> > +	unsigned long last_ts;
> > +};
> 
> Why isn't this either a 'struct device' itself, or why isn't the 'struct
> pci_device' embedded within it?  What controls the lifetime of this
> device?  Why doesn't it show up in sysfs?  Don't you want it to show up
> in the global device tree?
> 
> > +static DEFINE_PCI_DEVICE_TABLE(ntb_pci_tbl) = {
> > +	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_NTB_B2B_BWD)},
> > +	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_NTB_B2B_JSF)},
> > +	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_NTB_CLASSIC_JSF)},
> > +	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_NTB_RP_JSF)},
> > +	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_NTB_RP_SNB)},
> > +	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_NTB_B2B_SNB)},
> > +	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_NTB_CLASSIC_SNB)},
> > +	{0}
> > +};
> > +MODULE_DEVICE_TABLE(pci, ntb_pci_tbl);
> > +
> > +static struct ntb_device *ntbdev;
> 
> You can really only have just one of these in the whole system?  Is that
> wise?  Why isn't it dynamic and tied to the pci device itself as a
> child?

Good point, I will fix that up.

Thanks for the review!

> 
> thanks,
> 
> greg k-h
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