From: Cyril Chemparathy <cyril@ti.com>
To: linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] /dev/mem: use phys_addr_t for physical addresses
Date: Wed, 12 Sep 2012 22:54:27 +0000 [thread overview]
Message-ID: <505112A3.7080703@ti.com> (raw)
In-Reply-To: <20120912181503.GB12840@kroah.com>
Greg,
On 9/12/2012 2:15 PM, Greg KH wrote:
> On Wed, Sep 12, 2012 at 02:05:58PM -0400, Cyril Chemparathy wrote:
>> This patch fixes the /dev/mem driver to use phys_addr_t for physical
>> addresses. This is required on PAE systems, especially those that run
>> entirely out of >4G physical memory space.
>
> What is the symptom if this patch is not applied? Does it need to be
> backported to older kernels? If so, which ones?
>
As far as I can tell, this change only benefits platforms where lowmem
lies outside the 32-bit addressable range. On the ARM based KeyStone
platform, all of our memory is located above the 4GB limit at
0x8:0000:0000. On this platform, trying to read lowmem breaks as follows:
# dd if=/dev/mem of=/dev/null bs=4k count=1 skipƒ88608
dd: /dev/mem: Bad address
Assuming that we are unique in this regard (i.e. lowmem outside 4GB), I
don't see any reason to backport this to earlier kernels.
--
Thanks
- Cyril
WARNING: multiple messages have this Message-ID (diff)
From: cyril@ti.com (Cyril Chemparathy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] /dev/mem: use phys_addr_t for physical addresses
Date: Wed, 12 Sep 2012 18:54:27 -0400 [thread overview]
Message-ID: <505112A3.7080703@ti.com> (raw)
In-Reply-To: <20120912181503.GB12840@kroah.com>
Greg,
On 9/12/2012 2:15 PM, Greg KH wrote:
> On Wed, Sep 12, 2012 at 02:05:58PM -0400, Cyril Chemparathy wrote:
>> This patch fixes the /dev/mem driver to use phys_addr_t for physical
>> addresses. This is required on PAE systems, especially those that run
>> entirely out of >4G physical memory space.
>
> What is the symptom if this patch is not applied? Does it need to be
> backported to older kernels? If so, which ones?
>
As far as I can tell, this change only benefits platforms where lowmem
lies outside the 32-bit addressable range. On the ARM based KeyStone
platform, all of our memory is located above the 4GB limit at
0x8:0000:0000. On this platform, trying to read lowmem breaks as follows:
# dd if==/dev/mem of=/dev/null bs==4k count=1 skip=8388608
dd: /dev/mem: Bad address
Assuming that we are unique in this regard (i.e. lowmem outside 4GB), I
don't see any reason to backport this to earlier kernels.
--
Thanks
- Cyril
WARNING: multiple messages have this Message-ID (diff)
From: Cyril Chemparathy <cyril@ti.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: <linux-arm-kernel@lists.infradead.org>,
<linux-ia64@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-sh@vger.kernel.org>, <arnd@arndb.de>,
<dhowells@redhat.com>, <fenghua.yu@intel.com>,
<lethal@linux-sh.org>, <linux@arm.linux.org.uk>,
<nico@linaro.org>, <rob.herring@calxeda.com>,
<tony.luck@intel.com>, <tony@atomide.com>, <will.deacon@arm.com>
Subject: Re: [PATCH v2] /dev/mem: use phys_addr_t for physical addresses
Date: Wed, 12 Sep 2012 18:54:27 -0400 [thread overview]
Message-ID: <505112A3.7080703@ti.com> (raw)
In-Reply-To: <20120912181503.GB12840@kroah.com>
Greg,
On 9/12/2012 2:15 PM, Greg KH wrote:
> On Wed, Sep 12, 2012 at 02:05:58PM -0400, Cyril Chemparathy wrote:
>> This patch fixes the /dev/mem driver to use phys_addr_t for physical
>> addresses. This is required on PAE systems, especially those that run
>> entirely out of >4G physical memory space.
>
> What is the symptom if this patch is not applied? Does it need to be
> backported to older kernels? If so, which ones?
>
As far as I can tell, this change only benefits platforms where lowmem
lies outside the 32-bit addressable range. On the ARM based KeyStone
platform, all of our memory is located above the 4GB limit at
0x8:0000:0000. On this platform, trying to read lowmem breaks as follows:
# dd if==/dev/mem of=/dev/null bs==4k count=1 skip=8388608
dd: /dev/mem: Bad address
Assuming that we are unique in this regard (i.e. lowmem outside 4GB), I
don't see any reason to backport this to earlier kernels.
--
Thanks
- Cyril
next prev parent reply other threads:[~2012-09-12 22:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-12 18:05 [PATCH v2] /dev/mem: use phys_addr_t for physical addresses Cyril Chemparathy
2012-09-12 18:05 ` Cyril Chemparathy
2012-09-12 18:05 ` Cyril Chemparathy
2012-09-12 18:15 ` Greg KH
2012-09-12 18:15 ` Greg KH
2012-09-12 18:15 ` Greg KH
2012-09-12 22:54 ` Cyril Chemparathy [this message]
2012-09-12 22:54 ` Cyril Chemparathy
2012-09-12 22:54 ` Cyril Chemparathy
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