From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bjorn Helgaas Subject: Re: [RFC PATCH] PCI/portdrv: Support for subtractive decode bridge Date: Wed, 13 Feb 2019 13:11:32 -0600 Message-ID: <20190213191132.GI96272@google.com> References: <1544758829-10327-1-git-send-email-honghui.zhang@mediatek.com> <20190207151816.GI7268@google.com> <1549940249.4980.56.camel@mhfsdcap03> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1549940249.4980.56.camel@mhfsdcap03> Sender: linux-kernel-owner@vger.kernel.org To: Honghui Zhang Cc: lorenzo.pieralisi@arm.com, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, ryder.lee@mediatek.com, matthias.bgg@gmail.com, youlin.pei@mediatek.com, poza@codeaurora.org, fred@fredlawl.com, rafael.j.wysocki@intel.com, jianjun.wang@mediatek.com List-Id: linux-mediatek@lists.infradead.org On Tue, Feb 12, 2019 at 10:57:29AM +0800, Honghui Zhang wrote: > On Thu, 2019-02-07 at 09:18 -0600, Bjorn Helgaas wrote: > > On Fri, Dec 14, 2018 at 11:40:29AM +0800, honghui.zhang@mediatek.com wrote: > > > From: Honghui Zhang > > > > > > The Class Code for subtractive decode PCI-to-PCI bridge is 060401h, > > > change the class_mask values to make portdrv support this type bridge. > > > > I assume you have a Root Port or Switch Port that supports subtractive > > decode? I'm trying to understand how such a device would work. > > Yes, most of Mediatek's RC device have set the class type as 060401h as > HW default values, include mt2712 and mt7622. > > Those RC device work fine with all I have tried EP device except that > the portdrv was not attached to those device. But no scenario need those > service as far as I know. > > > Out of curiosity, can you show the "lspci -vv" output for the device > > and the downstream devices of interest? > > > lspci only read the class type 0604h, it does not care about the > subordinate values of the class type. I will put the "lspci -vv" output > at bottom of this mail. > > > Do you happen to know whether this functionality is configurable, > > e.g., is there some way software can enable or disable subtractive > > decode? I assume this would be some device-specific thing, because I > > can't find anything in the Bridge Control register or similar. The > > PCIe spec doesn't even contain the word "subtractive". > > Those class type values for Mediatek's RC has a register which could be > used to change its values. We never touch this backdoor register since > without the portdrv attached is fine, nobody ask for the port service > yet. > > I did some homework for the subtractive decode PCI-to-PCI bridge, and > did not found much more information about that. I guess those port > service should also support subtractive bridge since spec does not > forbidden that. OK, I guess that makes sense. > > The "PCI Express to PCI/PCI-X Bridge Specification", r1.0, says a PCI > > Express bridge (which would include Root Ports and Switch Ports) has a > > Class Code of 0x060400 (Non-Subtractive PCI-PCI Bridge) (sec 1.1). > > > > Sec 1.3.4 says subtractive decode on the primary interface is "not > > applicable or outside the scope of this spec". > # lspci -vvv > 00:01.0 Class 0604: Device 14c3:5396 > ... > > > Signed-off-by: Honghui Zhang > > > --- > > > drivers/pci/pcie/portdrv_pci.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c > > > index eef22dc..86926ea 100644 > > > --- a/drivers/pci/pcie/portdrv_pci.c > > > +++ b/drivers/pci/pcie/portdrv_pci.c > > > @@ -179,7 +179,7 @@ static void pcie_portdrv_err_resume(struct pci_dev *dev) > > > */ > > > static const struct pci_device_id port_pci_ids[] = { { > > > /* handle any PCI-Express port */ > > > - PCI_DEVICE_CLASS(((PCI_CLASS_BRIDGE_PCI << 8) | 0x00), ~0), > > > + PCI_DEVICE_CLASS(((PCI_CLASS_BRIDGE_PCI << 8) | 0x00), ~0x01), Can you please rework this slightly so it leaves the original entry alone and just *adds* a new entry that matches the subtractive-decode bridges? I think that will make it more obvious what's changing. > > > }, { /* end: all zeroes */ } > > > };