On 4/20/23 5:00 AM, Jonathan Cameron wrote:
On Wed, 19 Apr 2023 13:21:49 -0700
Dave Jiang <dave.jiang@xxxxxxxxx> wrote:
CXL spec v3.0 9.17.3 CXL Root Device Specific Methods (_DSM)
Add support to retrieve QTG ID via ACPI _DSM call. The _DSM call requires
an input of an ACPI package with 4 dwords (read latency, write latency,
read bandwidth, write bandwidth). The call returns a package with 1 WORD
that provides the max supported QTG ID and a package that may contain 0 or
more WORDs as the recommended QTG IDs in the recommended order.
Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
A few minor comments inline.
+/**
+ * cxl_acpi_evaluate_qtg_dsm - Retrieve QTG ids via ACPI _DSM
+ * @handle: ACPI handle
+ * @input: bandwidth and latency data
+ *
+ * Issue QTG _DSM with accompanied bandwidth and latency data in order to get
+ * the QTG IDs that falls within the performance data.
Falls within is a little vague. Perhaps something like
the QTG IDs that are suitable for the performance point in order of most suitable
to least suitable.
Thanks. I will update with your suggestion.
+ */
+struct qtg_dsm_output *cxl_acpi_evaluate_qtg_dsm(acpi_handle handle,
+ struct qtg_dsm_input *input)
+{
+ union acpi_object *out_obj, *out_buf, *pkg;
+ union acpi_object in_buf = {
+ .buffer = {
+ .type = ACPI_TYPE_BUFFER,
+ .pointer = (u8 *)input,
+ .length = sizeof(u32) * 4,
sizeof(*input)?
ok
Also, ACPI structures are always little endian. Do we need to be careful of that
here?
sigh yes. I will add in endieness handling for the patch.
+ },
+ };
+ union acpi_object in_obj = {
+ .package = {
+ .type = ACPI_TYPE_PACKAGE,
+ .count = 1,
+ .elements = &in_buf
+ },
+ };
+ struct qtg_dsm_output *output = NULL;
+ int len, rc, i;
+ u16 *max_qtg;
+
+ out_obj = acpi_evaluate_dsm(handle, &acpi_cxl_qtg_id_guid, 1, 1, &in_obj);
+ if (!out_obj)
+ return ERR_PTR(-ENXIO);
+
+ if (out_obj->type != ACPI_TYPE_PACKAGE) {
+ rc = -ENXIO;
+ goto err;
+ }
+
+ /* Check Max QTG ID */
+ pkg = &out_obj->package.elements[0];
+ if (pkg->type != ACPI_TYPE_BUFFER) {
+ rc = -ENXIO;
+ goto err;
+ }
+
+ if (pkg->buffer.length != sizeof(u16)) {
+ rc = -ENXIO;
+ goto err;
+ }
+ max_qtg = (u16 *)pkg->buffer.pointer;
+
+ /* Retrieve QTG IDs package */
+ pkg = &out_obj->package.elements[1];
+ if (pkg->type != ACPI_TYPE_PACKAGE) {
+ rc = -ENXIO;
+ goto err;
+ }
+
+ out_buf = &pkg->package.elements[0];
+ if (out_buf->type != ACPI_TYPE_BUFFER) {
+ rc = -ENXIO;
+ goto err;
+ }
+
+ len = out_buf->buffer.length;
+
+ /* It's legal to have 0 QTG entries */
+ if (len == 0)
+ goto out;
+
+ /* Malformed package, not multiple of WORD size */
+ if (len % sizeof(u16)) {
+ rc = -ENXIO;
+ goto out;
+ }
+
+ output = kmalloc(len + sizeof(*output), GFP_KERNEL);
+ if (!output) {
+ rc = -ENOMEM;
+ goto err;
+ }
+
+ output->nr = len / sizeof(u16);
+ memcpy(output->qtg_ids, out_buf->buffer.pointer, len);
+
+ for (i = 0; i < output->nr; i++) {
+ if (output->qtg_ids[i] > *max_qtg)
+ pr_warn("QTG ID %u greater than MAX %u\n",
+ output->qtg_ids[i], *max_qtg);
+ }
+
+out:
+ ACPI_FREE(out_obj);
+ return output;
+
+err:
+ ACPI_FREE(out_obj);
+ return ERR_PTR(rc);
Why not combine these with something like
return IS_ERR(rc) ? ERR_PTR(rc) : output;
I'm fine with leaving as it is, if this is common style for these
sorts of ACPI functions.
I'll combine it. But if I just set output to ERR_PTR(errno) for all the
error cases then we can just return output directly without checking?
+}
+EXPORT_SYMBOL_NS_GPL(cxl_acpi_evaluate_qtg_dsm, CXL);
