Re: [PATCH 1/2] kernel/resource: Add new flag IORESOURCE_SHARED

[Ricardo Ribalda Delgado]

Hello Grant

On Mon, Jun 8, 2015 at 8:23 PM, Grant Likely <grant.likely@xxxxxxxxxx> wrote:
> On Fri,  5 Jun 2015 12:51:17 +0200
> , Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx>
>  wrote:
>> Some device tree platforms have not defined correctly their memory
>> resources (i.e. Overlapping or duplication of resources).
>> To avoid this issue we have historically avoided to add their resources to
>> the resource tree. This leads to code duplication and oops when trying to
>> unload dynamically a device tree (feature introduced recently).
>>
>> This new flag tells the resource system that a resource can be shared by
>> multiple owners, so we can support device trees with problems at the
>> same time that we do not duplicate code or crash when unloading the
>> device tree.
>>
>> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx>
>> ---
>
> I'm really not comfortable with this change. The resource tree code is
> complicated enough as is. Adding this exception case quite probably adds
> corner cases that aren't property dealt with. If two regions overlay,
> and then request_region is called? Which region does it become a child
> of? And that's just off the top of my head. I don't want to hack in
> changes to the resource code for what is a corner case.

I see your concern, perhaps you could provide a testcase and we can
find out if it fails or not. So far I have tested a device tree with
two devices on the same memory region, each device managed by a
driver.

I can load and unload the device tree perfectly.

>
> g.
>
>>  include/linux/ioport.h | 1 +
>>  kernel/resource.c      | 6 ++++--
>>  2 files changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
>> index 388e3ae94f7a..f4d992381529 100644
>> --- a/include/linux/ioport.h
>> +++ b/include/linux/ioport.h
>> @@ -49,6 +49,7 @@ struct resource {
>>  #define IORESOURCE_WINDOW    0x00200000      /* forwarded by bridge */
>>  #define IORESOURCE_MUXED     0x00400000      /* Resource is software muxed */
>>
>> +#define IORESOURCE_SHARED    0x04000000      /* Resource can be shared */
>>  #define IORESOURCE_EXCLUSIVE 0x08000000      /* Userland may not map this resource */
>>  #define IORESOURCE_DISABLED  0x10000000
>>  #define IORESOURCE_UNSET     0x20000000      /* No address assigned yet */
>> diff --git a/kernel/resource.c b/kernel/resource.c
>> index 90552aab5f2d..4a3626489b62 100644
>> --- a/kernel/resource.c
>> +++ b/kernel/resource.c
>> @@ -210,6 +210,7 @@ static struct resource * __request_resource(struct resource *root, struct resour
>>       resource_size_t start = new->start;
>>       resource_size_t end = new->end;
>>       struct resource *tmp, **p;
>> +     bool root_shared = root && root->flags & IORESOURCE_SHARED;
>>
>>       if (end < start)
>>               return root;
>> @@ -220,14 +221,15 @@ static struct resource * __request_resource(struct resource *root, struct resour
>>       p = &root->child;
>>       for (;;) {
>>               tmp = *p;
>> -             if (!tmp || tmp->start > end) {
>> +             if (!tmp || tmp->start > end ||
>> +                     (root_shared && tmp->start > start)) {
>>                       new->sibling = tmp;
>>                       *p = new;
>>                       new->parent = root;
>>                       return NULL;
>>               }
>>               p = &tmp->sibling;
>> -             if (tmp->end < start)
>> +             if (tmp->end < start || root_shared)
>>                       continue;
>>               return tmp;
>>       }
>> --
>> 2.1.4
>>
>



-- 
Ricardo Ribalda
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