The ELD baseline block reserves bytes 8..15 for a 64-bit Port_ID that identifies the source port of the audio endpoint. drm_edid_to_eld() leaves the field zero, and no driver fills it in, so it carries no information.
When two identical monitors are connected, their ELDs are then byte-identical, and userspace has no passive way to tell which HDMI/DP PCM belongs to which DRM connector. The only workaround is to toggle the connector audio property and watch which ELD goes away, which disrupts the endpoint. Add a helper that drivers can use to fill in Port_ID with a common layout: bits 63:48 - PCI domain of the DRM device bits 47:32 - PCI bus/device/function of the DRM device bits 31:0 - DRM connector object ID Userspace can read the connector object ID directly from KMS, and the PCI address tells GPUs apart in multi-GPU systems. For non-PCI devices the upper half is left zero. The split between a 16-bit PCI BDF in the upper half and a per-device display identifier in the lower half follows the Port_ID layout documented for the AMD Azalia sink info registers in dce_audio.c. Signed-off-by: Kai Vehmanen <[email protected]> --- drivers/gpu/drm/drm_eld.c | 42 +++++++++++++++++++++++++++++++++++++++ include/drm/drm_eld.h | 3 +++ 2 files changed, 45 insertions(+) diff --git a/drivers/gpu/drm/drm_eld.c b/drivers/gpu/drm/drm_eld.c index c0428d07de53..baebece7b4ed 100644 --- a/drivers/gpu/drm/drm_eld.c +++ b/drivers/gpu/drm/drm_eld.c @@ -4,7 +4,11 @@ */ #include <linux/export.h> +#include <linux/pci.h> +#include <linux/unaligned.h> +#include <drm/drm_connector.h> +#include <drm/drm_device.h> #include <drm/drm_edid.h> #include <drm/drm_eld.h> @@ -55,3 +59,41 @@ int drm_eld_sad_set(u8 *eld, int sad_index, const struct cea_sad *cta_sad) return 0; } EXPORT_SYMBOL(drm_eld_sad_set); + +/** + * drm_eld_set_port_id - set the ELD Port_ID for a connector + * @eld: ELD buffer + * @connector: connector the ELD belongs to + * + * drm_edid_to_eld() leaves the 64-bit Port_ID field of the ELD baseline + * block zero. Drivers can use this helper to fill it in with a value + * that identifies the audio endpoint, so that userspace can associate an + * ELD, and the PCM device it belongs to, with a DRM connector, even when + * identical sinks are connected to multiple outputs. + * + * The Port_ID is stored in little-endian byte order, with the layout: + * + * - bits 63:48 - PCI domain of the DRM device, truncated to 16 bits + * - bits 47:32 - PCI bus/device/function of the DRM device + * - bits 31:0 - DRM connector object ID + * + * For non-PCI devices bits 63:32 are zero. + * + * The connector object ID is only stable for the lifetime of the + * connector, so userspace must look it up at runtime, and not store it. + */ +void drm_eld_set_port_id(u8 *eld, const struct drm_connector *connector) +{ + struct device *dev = connector->dev->dev; + u64 port_id = connector->base.id; + + if (dev && dev_is_pci(dev)) { + struct pci_dev *pdev = to_pci_dev(dev); + + port_id |= (u64)(pci_domain_nr(pdev->bus) & 0xffff) << 48 | + (u64)pci_dev_id(pdev) << 32; + } + + put_unaligned_le64(port_id, &eld[DRM_ELD_PORT_ID]); +} +EXPORT_SYMBOL(drm_eld_set_port_id); diff --git a/include/drm/drm_eld.h b/include/drm/drm_eld.h index 0a88d10b28b0..de0478720721 100644 --- a/include/drm/drm_eld.h +++ b/include/drm/drm_eld.h @@ -9,6 +9,7 @@ #include <linux/types.h> struct cea_sad; +struct drm_connector; /* ELD Header Block */ #define DRM_ELD_HEADER_BLOCK_SIZE 4 @@ -80,6 +81,8 @@ static inline int drm_eld_mnl(const u8 *eld) int drm_eld_sad_get(const u8 *eld, int sad_index, struct cea_sad *cta_sad); int drm_eld_sad_set(u8 *eld, int sad_index, const struct cea_sad *cta_sad); +void drm_eld_set_port_id(u8 *eld, const struct drm_connector *connector); + /** * drm_eld_sad - Get ELD SAD structures. * @eld: pointer to an eld memory structure with sad_count set -- 2.43.0
