linux-kernel - Re: [PATCH 2/6] device/pci: add cmdmem cap to pci

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Message-ID: <20200331172459.GA1841577@kroah.com>
Date:   Tue, 31 Mar 2020 19:24:59 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     vkoul@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, bhelgaas@...gle.com, arnd@...db.de,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        dmaengine@...r.kernel.org, dan.j.williams@...el.com,
        ashok.raj@...el.com, fenghua.yu@...el.com,
        linux-pci@...r.kernel.org, tony.luck@...el.com, jing.lin@...el.com,
        sanjay.k.kumar@...el.com
Subject: Re: [PATCH 2/6] device/pci: add cmdmem cap to pci_dev

On Tue, Mar 31, 2020 at 10:07:07AM -0700, Dave Jiang wrote:
> 
> On 3/31/2020 3:04 AM, Greg KH wrote:
> > On Mon, Mar 30, 2020 at 02:27:00PM -0700, Dave Jiang wrote:
> > > Since the current accelerator devices do not have standard PCIe capability
> > > enumeration for accepting ENQCMDS yet, for now an attribute of pdev->cmdmem has
> > > been added to struct pci_dev.  Currently a PCI quirk must be used for the
> > > devices that have such cap until the PCI cap is standardized. Add a helper
> > > function to provide the check if a device supports the cmdmem capability.
> > > 
> > > Such capability is expected to be added to PCIe device cap enumeration in
> > > the future.
> > > 
> > > Signed-off-by: Dave Jiang <dave.jiang@...el.com>
> > > ---
> > >   drivers/base/core.c    |   13 +++++++++++++
> > >   include/linux/device.h |    2 ++
> > >   include/linux/pci.h    |    1 +
> > >   3 files changed, 16 insertions(+)
> > > 
> > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > index dbb0f9130f42..cd9f5b040ed4 100644
> > > --- a/drivers/base/core.c
> > > +++ b/drivers/base/core.c
> > > @@ -27,6 +27,7 @@
> > >   #include <linux/netdevice.h>
> > >   #include <linux/sched/signal.h>
> > >   #include <linux/sysfs.h>
> > > +#include <linux/pci.h>
> > >   #include "base.h"
> > >   #include "power/power.h"
> > > @@ -3790,3 +3791,15 @@ int device_match_any(struct device *dev, const void *unused)
> > >   	return 1;
> > >   }
> > >   EXPORT_SYMBOL_GPL(device_match_any);
> > > +
> > > +bool device_supports_cmdmem(struct device *dev)
> > > +{
> > > +	struct pci_dev *pdev;
> > > +
> > > +	if (!dev_is_pci(dev))
> > > +		return false;
> > > +
> > > +	pdev = to_pci_dev(dev);
> > > +	return pdev->cmdmem;
> > > +}
> > > +EXPORT_SYMBOL_GPL(device_supports_cmdmem);
> > Why would a pci-specific function like this be ok to have in the driver
> > core?  Please keep it in the pci core code instead.
> 
> The original thought was to introduce a new arch level memory mapping
> semantic.

Please do not.  Also, that's not what you are doing here from what I can
tell.

> If you feel this should be PCI exclusive, should we make the ioremap
> routines for this memory type pci specific as well?

Why wouldn't it be?  Is this needed anywhere else?

thanks,

greg k-h