Date: Thu, 18 Jun 2015 11:01:03 -0700
From: Guenter Roeck <linux@roeck-us.net>
To: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>,
        Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] PCI: Only enable IO window if supported
Message-ID: <20150618180103.GA23809@roeck-us.net>
References: <1432342336-25832-1-git-send-email-linux@roeck-us.net>
 <20150527210447.GY32152@google.com>
 <20150528022332.GA23724@roeck-us.net>
 <20150528124112.GJ10210@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150528124112.GJ10210@google.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
X-Authenticated_sender: guenter@roeck-us.net
X-OutGoing-Spam-Status: No, score=-1.0
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net
X-AntiAbuse: Original Domain - vger.kernel.org
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain - roeck-us.net
X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: guenter@roeck-us.net
X-Source: 
X-Source-Args: 
X-Source-Dir: 
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1631
Lines: 38

On Thu, May 28, 2015 at 07:41:12AM -0500, Bjorn Helgaas wrote:
> 
> > > I'd like res->flags to reflect the capabilities of the hardware, not
> > > whether the window is currently enabled.
> > > 
> > Flag bits seem to be all taken. Could we use IORESOURCE_DISABLED for that
> > purpose, or could that cause conflicts elsewhere ?
> 
> Yes, I think IORESOURCE_DISABLED would be appropriate for any I/O windows
> below a host bridge that doesn't support I/O space.
> 
I integrated Lorenzo's patch and tried to get this working.

Problem is that the use of a resource is widely checked with "!res->flags"
throughout the code. That would have to be changed to something like
"(!res->flags || (res->flags & IORESOURCE_DISABLED))" whereever it is used.

I tried going with "!res->flags" instead, but have not been able to get it
to work realiably; it is just very difficult to distinguish if "!res->flags"
means that the resource has not yet been assigned or if it means that it is not
supported.

The correct approach, in my opinion, would be to go with IORESOURCE_DISABLED
and make the necessary changes whereever needed. Effectively this means to
replace the "!res->flags" check with something like pci_res_used() [ pick
your preferred name ] and define it as

#define pci_res_used(res) ((res)->flags && !((res)->flags & IORESOURCE_DISABLED))

Is that the right direction ?

Thanks,
Guenter
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/