[RFC 1/1] ARM: imx6q: move clock register map to machine_desc.map_io

Eric Miao eric.miao at linaro.org
Thu Nov 17 04:03:15 EST 2011

On Thu, Nov 17, 2011 at 5:07 PM, Shawn Guo <shawn.guo at freescale.com> wrote:
> On Thu, Nov 17, 2011 at 08:44:53AM +0000, Russell King - ARM Linux wrote:
>> On Thu, Nov 17, 2011 at 11:20:13AM +0800, Shawn Guo wrote:
>> > On Thu, Nov 17, 2011 at 10:56:53AM +0800, Eric Miao wrote:
>> > > On Thu, Nov 17, 2011 at 9:50 AM, Richard Zhao <richard.zhao at linaro.org> wrote:
>> > > > If the map is in machine_desc.timer.init, the registers will not be
>> > > > able to access after bootup (probably after "Freeing init memory").
>> > >
>> > > Given that devicemaps_init() does additional work after creating
>> > > the mapping, flushing TLB and cache, machine_desc->map_io() is
>> > > what I assume the best place for these static IO mappings than
>> > > elsewhere.
>> > >
>> > > Shawn?
>> > >
>> > I'm still trying to understand what happened.  I do not understand
>> > how the map can become unusable after "Freeing init memory".  Also
>> > I can not reproduce the problem on my side.
>> It's very simple.  iotable_init() allocates memory using memblock.
>> memblock marks the memory it allocates in its reserved map.  At the
>> end of map_io(), the information stored inside memblock is transferred
>> to bootmem and then the normal page allocator.  Once this is done,
>> memblock must not be changed because there is no way to couple any
>> further memblock allocations into the normal page allocator.
>> Look.  I've made this point before and I'm getting pissed off with
>> people who think they know better.  The callbacks in the machine
>> descriptor are NAMED.  They're NAMED for a reason - they have a PURPOSE
>> and that PURPOSE is well defined because there are DEPENDENCIES there.
>> They tell you what you SHOULD be doing in there.  Doing something else
>> will result in BAD THINGS happening.
>> If people can't understand this, then the only solution is to make the
>> backing functions for this stuff (like iotable_init() etc) BUG() when
>> they're abused.  That means adding a lot more checks and slowing down
>> the boot because people seem to be incapable of comprehending that
>> initialisation needs to be done in a well defined order.
> Russell,
> Thanks for help understand the issue.
> Richard,
> Please revise the patch to introduce function like imx6q_clock_map_io()
> to be called in imx6q_map_io().

Or simply imx6q_io_desc[], and doing a iotable_init() for all (and
considering ANATOP not necessarily include clocks registers only)
other possible static IO mappings in the future.

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