linux-kernel - Re: [patch 00/37] PNP resource

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Date:	Thu, 03 Apr 2008 19:12:16 +0200
From:	Rene Herman <rene.herman@...access.nl>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Adam Belay <ambx1@....rr.com>,
	Li Shaohua <shaohua.li@...el.com>,
	Matthieu Castet <castet.matthieu@...e.fr>,
	Thomas Renninger <trenn@...e.de>,
	Jaroslav Kysela <perex@...ex.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 00/37] PNP resource_table cleanups, v2

On 03-04-08 18:43, Bjorn Helgaas wrote:

> On Thursday 03 April 2008 09:54:51 am Rene Herman wrote:
>> However, now that you made me look closer and in context -- there's actually 
>> a possibly somewhat serious problem here.
>>
>> isapnp_read_resources() stores the resources as read from the hardware at 
>> the index in the table that matches the actual index in the hardware and 
>> isapnp_set_resources() stores them back into those same hardware indices.
>>
>> Now by using pnp_add_foo_resource() which just scans for the first _UNSET 
>> resource, the resources might not end up in the same linear position in 
>> table/list if intermediate resources were unset in hardware (!ret). A 
>> subsequent isapnp_set_resources() would them restore the value to the wrong 
>> hardware index.
>>
>> The IORESOURCE_ flags currently reserve too few bits (IORESOURCE_BITS,  8) 
>> to be able to store the hardware index: IORESOURCE_MEM and IORESOURCE_DMA 
>> need 2 and 1 respectively and there are 1 and 0 available respectively. It's 
>> ofcourse possible to hijack a few more bits in IORESOURCE_ flags but you're 
>> turning this into a list. I suppose the idea is to make it a simple list of 
>> struct resource, but perhaps a resource-private "driver_data" sort of field 
>> comes in handy for more than this already? Swiping more of IORESOURCE_ is a 
>> bit ugly...
>>
>> In any case, I missed this, but ISAPnP is still (at least in principle) 
>> broken with the current set therefore.
> 
> Hmm...  you're right.  And I think it could bite PNPBIOS and PNPACPI
> as well -- they don't read/write hardware registers directly, but the
> firmware still depends on preserving the resource order.  I'll have to
> ponder that for a while.

Both PNPBIOS and PNPACPI should be fine it seems:

pnpbios_get_resources()
   pnpbios_read_resources_from_node()
     pnpbios_parse_allocated_resource_data()
       pnpbios_parse_allocated_irqresource()
       pnpbios_parse_allocated_dmaresource()
       pnpbios_parse_allocated_ioresource()
       pnpbios_parse_allocated_memresource()

where the latter do the same scan for the first _UNSET resource as the new 
code does. Same thing for ACPI in the path

pnpacpi_get_resources()
   pnpacpi_parse_allocated_resource()
      pnpacpi_allocated_resource()
        pnpacpi_parse_allocated_irqresource()
        pnpacpi_parse_allocated_dmaresource()
        pnpacpi_parse_allocated_ioresource()
        pnpacpi_parse_allocated_memresource()
        pnpacpi_parse_allocated_address_space()
          pnpacpi_parse_allocated_memresource()

Rene.
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