Claude review: firmware: qcom: Add a generic PAS service

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This is the core abstraction patch and has the most significant issues.

**Race condition in ops_ptr access.** Every API function does a bare pointer check then dereference:

```c
int qcom_pas_init_image(u32 pas_id, const void *metadata, size_t size,
			struct qcom_pas_context *ctx)
{
	if (ops_ptr)
		return ops_ptr->init_image(ops_ptr->dev, pas_id,
					   metadata, size, ctx);
	return -ENODEV;
}
```

But `qcom_pas_ops_unregister()` can set `ops_ptr = NULL` concurrently. There's no RCU, no mutex, no refcounting — just `smp_store_release`/`smp_load_acquire` in the register/unregister/is_available paths. However, the actual API functions use bare `ops_ptr` reads without acquire semantics. This means a client could pass the `if (ops_ptr)` check, then the backend gets unregistered, and the `ops_ptr->init_image(...)` call dereferences freed/NULL memory. At minimum, all reads of `ops_ptr` in the API functions should use `smp_load_acquire`, and ideally an `srcu_read_lock` / refcount should protect the critical section.

**`qcom_pas_ops_register()` calls `qcom_pas_is_available()` which does `smp_load_acquire` but then the subsequent `smp_store_release` in the else branch is fine. However, two concurrent registrations are not protected — there's no lock, just a TOCTOU check:**

```c
void qcom_pas_ops_register(struct qcom_pas_ops *ops)
{
	if (!qcom_pas_is_available())
		smp_store_release(&ops_ptr, ops);
	else
		pr_err("qcom_pas: ops already registered\n");
}
```

**`qcom_scm_pas_auth_and_reset` doc comment typo** — the kernel-doc says `qcom_scm_pas_auth_and_reset` but the function is `qcom_pas_auth_and_reset` (line 663 in the new file).

**Return type mismatch on `get_rsc_table` callback.** The ops struct declares `void *(*get_rsc_table)(...)` but the public API `qcom_pas_get_rsc_table()` returns `struct resource_table *`. The implicit cast works but is inconsistent and should be explicit.

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