Re: [PATCH v4 5/9] drivers: base: cacheinfo: arm64: Add support for ACPI based firmware tables

From: Jeremy Linton
Date: Mon Nov 20 2017 - 13:02:07 EST

On 11/20/2017 10:56 AM, Sudeep Holla wrote:


* case there's no explicit cache node or the cache node itself in the
* device tree
+ * @firmware_node: Shared with of_node. When not using DT, this may contain
+ * pointers to other firmware based values. Particularly ACPI/PPTT
+ * unique values.
* @disable_sysfs: indicates whether this node is visible to the user via
* sysfs or not
* @priv: pointer to any private data structure specific to particular
@@ -64,8 +67,10 @@ struct cacheinfo {
#define CACHE_ID BIT(4)
- struct device_node *of_node;
+ union {
+ struct device_node *of_node;
+ void *firmware_node;
+ };

I would prefer
struct device_node *of_node;
changed to
struct fwnode_handle *fwnode;

You can then have
struct pptt_fwnode {
/*below fwnode allocated using acpi_alloc_fwnode_static */
struct fwnode_handle *fwnode;

This gives a good starting point to abstract DT and ACPI.

If not now, we can later implement fwnode.ops=pptt_cache_ops and then
use get property for both DT and ACPI.

I'm obviously confused why this keeps coming up. On the surface it sounds like a good idea. But then, given that I've actually implemented a portion of it, what becomes clear is that the PPTT isn't a good match. Converting the OF routines to use the fwnode is fairly straightforward, but that doesn't help the ACPI situation other than to create a lot of misleading code (and the possibility of creating nonstandard DSDT entries). The fact that this hasn't been done for other tables MADT/SLIT/SRAT/etc makes me wonder why we should do it for the PPTT?

Particularly, when one considers fwnode is more a DSDT<->DT abstraction and thus has a lot of API surface that simply doesn't make any sense given the PPTT binary tree structure. Given that most of the fwnode routines are translating string properties (for example fwnode_property_read_string()) it might be possible to build a translator of some form which takes DT style properties and attempts to map them to the ACPI PPTT tree. What this adds I can't fathom, beyond the fact that suddenly the fwnode interface is a partial/brittle implementation where a large subset of the fwnode_operations will tend to be degenerate cases. The result likely will be a poorly implemented translator which breaks or is meaningless over a large part of the fwnode API surface.