On Mon, Dec 02, 2013 at 05:59:56PM +0000, Kumar Gala wrote: > > On Dec 2, 2013, at 11:50 AM, Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > > > On Mon, Dec 02, 2013 at 05:28:41PM +0000, Kumar Gala wrote: > >> > >> On Dec 2, 2013, at 10:20 AM, Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > >> > >>> On ARM systems the cache topology cannot be probed at runtime, in > >>> particular, it is impossible to probe which CPUs share a given cache > >>> level. Power management software requires this knowledge to implement > >>> optimized power down sequences, hence this patch adds a document that > >>> defines the DT cache bindings for ARM systems. The bindings are compliant > >>> with ePAPR (PowerPC bindings), and rely on the cache bindings already > >>> standardized in the ePAPR v1.1 document; ARM required updates are underlined > >>> in the binding document. > >>> > >>> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> > >>> --- > >>> Documentation/devicetree/bindings/arm/cache.txt | 25 +++++++++++++++++++++++++ > >>> 1 file changed, 25 insertions(+) > >>> create mode 100644 Documentation/devicetree/bindings/arm/cache.txt > >>> > >>> diff --git a/Documentation/devicetree/bindings/arm/cache.txt b/Documentation/devicetree/bindings/arm/cache.txt > >>> new file mode 100644 > >>> index 0000000..009cddb > >>> --- /dev/null > >>> +++ b/Documentation/devicetree/bindings/arm/cache.txt > >>> @@ -0,0 +1,25 @@ > >>> +========================================== > >>> +ARM processors cache binding description > >>> +========================================== > >>> + > >>> +Device tree bindings for ARM processor caches adhere to the cache bindings > >>> +described in [3], in section 3.8 for multi-level and shared caches. > >>> + > >>> +On ARM, internal caches cannot be described in the cpu node but require > >>> +specific nodes marked with compatible string set to "cache" (see [3], > >>> +section 3.8). > >> > >> can you explain why > > > > ARM v7 and v8 processors have a concept of cache levels which is valid > > even for internal caches. So either we add a cache-level property to > > internal caches or we do not use them for ARM. > > There isn't anything precluding a cachel-level property for internal caches. > > > On top of that the definition of internal caches in the ePAPR is not > > well defined (for ARM) (what if you have multiple levels of internal > > caches ? - do we describe just L1 in the cpu node ?). > > ePAPR has examples of multiple level's of internal cache in the cpu node. Where ? 3.7.3 (ePAPR v1.1) Internal (L1) Cache properties ? I do not think so. It does by using the definitions in 3.8 "Multi level and shared caches". So, since the cache bindings in 3.8 allow to describe a cache hierarchy on ARM, that's what I used. Declaring L1 in the CPU node buys us nothing, so I do not think there is a point in using it on ARM. That's why instead of changing the bindings for internal (L1) caches to require cache-level we should just ignore them IMHO. ePAPR v1.1 contains a bug (example page 47 - line 47) since a cpu node cannot contain a cache-level property, that's not a property of internal caches and it has to be declared in a node with: compatible = "cache"; unless my understanding of ePAPR is wrong. All I am saying is that multi-level cache bindings can be used to describe all cache hierarchies for ARM, we do not need internal (L1) cache bindings at all, it is just legacy stuff. Lorenzo -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
