On Fri, Nov 09, 2012 at 05:00:54PM +0100, Christian König wrote:
On 09.11.2012 16:45, Rafał Miłecki wrote:
2012/11/9 Thierry Reding thierry.reding@avionic-design.de:
+/* all fields little endian */ +struct hdmi_audio_infoframe {
/* PB0 */u8 csum;/* PB1 */unsigned cc:3; /* channel count */unsigned res1:1;unsigned ct:4; /* coding type *//* PB2 */unsigned ss:2; /* sample size */unsigned sf:3; /* sample frequency */unsigned res2:3;/* PB3 */unsigned cxt:5; /* coding extention type */unsigned res3:3;/* PB4 */u8 ca; /* channel/speaker allocation *//* PB5 */unsigned res5:3;unsigned lsv:4; /* level shift value */unsigned dm_inh:1; /* downmix inhibit *//* PB6-10 reserved */u8 res6;u8 res7;u8 res8;u8 res9;u8 res10;+} __packed;
I was told it won't work on different endian devices. See [RFC][PATCH] drm/radeon/hdmi: define struct for AVI infoframe http://lists.freedesktop.org/archives/dri-devel/2012-May/022544.html
Yeah, that's indeed true. And honestly adding just another implementation of the HDMI info frames sounds like somebody should finally sit down and implement it in a common drm_hdmi.c
So I've been looking at what most other implementations do and it seems a lot just fill the AVI infoframe with zeroes while only a few actually try to put useful information in them. Still in order to plan for a generic solution, I thought maybe something like the below set of structures and functions could work:
/* * Structure that contains the infoframe fields in a form that allows them to * be easily accessed from C code. */ struct hdmi_avi_infoframe;
/* * DRM helper to fill a struct hdmi_avi_infoframe with information taken from * a struct drm_display_mode. Fields that cannot automatically be derived by * looking at a struct drm_display_mode are set to the default values. */ int drm_hdmi_avi_infoframe_from_display_mode(struct hdmi_avi_infoframe *frame, struct drm_display_mode *mode);
/* * Packs the struct hdmi_avi_infoframe into a binary buffer that can be * programmed to the hardware-specific registers. */ ssize_t hdmi_avi_infoframe_pack(struct hdmi_avi_infoframe *frame, void *buffer, size_t size);
Such a scheme would allow DRM drivers to call the helper and tweak the fields in the structure if the want or need to and call the packing function to obtain a buffer that they can write to the controller.
Does that sound at all reasonable?
Thierry