RFC: Improved handling of presets ================================= This RFC attempts to resolve the issues raised by this thread a few months ago: http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg33981.html The last post in this thread did a good job of summarizing the discussion: http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg34190.html I think it is time to revisit this problem. It basically boils down to the fact that the current preset API is too limited and somewhat awkward and I agree with that. Now, I really do not like the idea of creating a preset2 API. Instead I think it is better to extend the current dv_timings API with new ioctls: VIDIOC_QUERY_DV_TIMINGS VIDIOC_ENUM_DV_TIMINGS VIDIOC_DV_TIMINGS_CAP These form a superset of the preset API and once this is in place we can deprecate some or all of the preset ioctls and eventually remove them (say in one or two years). Here is the current definition of the v4l2_dv_timings struct from videodev2.h: /* BT.656/BT.1120 timing data */ struct v4l2_bt_timings { __u32 width; /* width in pixels */ __u32 height; /* height in lines */ __u32 interlaced; /* Interlaced or progressive */ __u32 polarities; /* Positive or negative polarity */ __u64 pixelclock; /* Pixel clock in HZ. Ex. 74.25MHz->74250000 */ __u32 hfrontporch; /* Horizpontal front porch in pixels */ __u32 hsync; /* Horizontal Sync length in pixels */ __u32 hbackporch; /* Horizontal back porch in pixels */ __u32 vfrontporch; /* Vertical front porch in pixels */ __u32 vsync; /* Vertical Sync length in lines */ __u32 vbackporch; /* Vertical back porch in lines */ __u32 il_vfrontporch; /* Vertical front porch for bottom field of * interlaced field formats */ __u32 il_vsync; /* Vertical sync length for bottom field of * interlaced field formats */ __u32 il_vbackporch; /* Vertical back porch for bottom field of * interlaced field formats */ __u32 reserved[16]; } __attribute__ ((packed)); /* Interlaced or progressive format */ #define V4L2_DV_PROGRESSIVE 0 #define V4L2_DV_INTERLACED 1 /* Polarities. If bit is not set, it is assumed to be negative polarity */ #define V4L2_DV_VSYNC_POS_POL 0x00000001 #define V4L2_DV_HSYNC_POS_POL 0x00000002 /* DV timings */ struct v4l2_dv_timings { __u32 type; union { struct v4l2_bt_timings bt; __u32 reserved[32]; }; } __attribute__ ((packed)); /* Values for the type field */ #define V4L2_DV_BT_656_1120 0 /* BT.656/1120 timing type */ This API allows you to set and get all the timings details. Its current use is to allow userspace to set non-standard timings and it is used only in the dm646x davinci drivers at the moment. I propose the following additions: 1) Add a standards field to v4l2_bt_timings: __u32 standards; Currently I have four standards: #define V4L2_DV_BT_STD_CEA861 (1 << 0) #define V4L2_DV_BT_STD_DMT (1 << 1) /* VESA Discrete Monitor Timings */ #define V4L2_DV_BT_STD_CVT (1 << 2) /* VESA Coordinated Video Timings */ #define V4L2_DV_BT_STD_GTF (1 << 3) /* VESA Generalized Timings Formula */ A particular timing can be part of 0 or more standards. Both CVT and GTF timings have a so-called 'reduced blanking' mode. It would be nice to represent this with a flag somewhere. I guess we need a flags field for that. The 'polarities' field really should have been called a 'flags' field. Oh well... 2) Create a VIDIOC_ENUM_DV_TIMINGS ioctl: struct v4l2_enum_dv_timings { __u32 index; char name[32]; struct v4l2_dv_timings timings; __u32 reserved[]; }; #define VIDIOC_ENUM_DV_TIMINGS _IOWR('V', XX, struct v4l2_enum_dv_timings) This ioctl enumerates over all discrete supported timings and returns their name and timings. The timings field can be used as an input to S_DV_TIMINGS. The timings in this enumeration are guaranteed to be supported by the hardware. However, other custom timings may be supported as well (see my proposal for VIDIOC_DV_TIMINGS_CAP). 3) Create a VIDIOC_QUERY_DV_TIMINGS ioctl: struct v4l2_query_dv_timings { __u32 state; __u32 index; struct v4l2_dv_timings timings; __u32 reserved[]; }; #define V4L2_QUERY_STATE_NO_TIMINGS 0 #define V4L2_QUERY_STATE_UNSUPP_TIMINGS 1 #define V4L2_QUERY_STATE_SUPP_TIMINGS 2 #define VIDIOC_QUERY_DV_TIMINGS _IOR('V', XX, struct v4l2_query_dv_timings) There are three states: 1 - no timings could be detected. Call ENUM_INPUT to find out why. 2 - timings could be detected, and the timings struct is filled in, but they are not supported by other parts of the hardware. Call DV_TIMINGS_CAP and check the timings against the capabilities to find out why. 3 - timings are detected and are supported. The index can be used with ENUM_DV_TIMINGS to get the name. If the timings are not part of the enumerated timings list, then index is set to 0xffffffff (or at least some value that will cause ENUM_DV_TIMINGS to return EINVAL). That value would be represented by a macro such as V4L2_QUERY_UNKNOWN_INDEX. 4) Create a VIDIOC_DV_TIMINGS_CAP ioctl: /* BT.656/BT.1120 timing capabilities */ struct v4l2_bt_timings_cap { __u32 min_width; /* width in pixels */ __u32 max_width; /* width in pixels */ __u32 min_height; /* height in lines */ __u32 max_height; /* height in lines */ __u64 min_pixelclock; /* Pixel clock in HZ. Ex. 74.25MHz->74250000 */ __u64 max_pixelclock; /* Pixel clock in HZ. Ex. 74.25MHz->74250000 */ __u32 standards; /* Supported standards */ __u32 flags; /* Interlaced or progressive */ __u32 reserved[16]; } __attribute__ ((packed)); /* Supports interlaced formats */ #define V4L2_DV_BT_CAP_INTERLACED (1 << 0) /* Supports progressive formats */ #define V4L2_DV_BT_CAP_PROGRESSIVE (1 << 1) /* Supports reduced blanking formats */ #define V4L2_DV_BT_CAP_REDUCED_BLANKING (1 << 2) /* Supports custom formats */ #define V4L2_DV_BT_CAP_CUSTOM (1 << 3) /* DV timings capabilities */ struct v4l2_dv_timings_cap { __u32 type; union { struct v4l2_bt_timings_cap bt; __u32 reserved[32]; }; } __attribute__ ((packed)); #define VIDIOC_DV_TIMINGS_CAP _IOWR('V', XX, struct v4l2_dv_timings_cap) This ioctl can be used to query the driver for the supported capabilities. Most speak for themselves. If V4L2_DV_BT_CAP_CUSTOM is not set, then only the timings from ENUM_DV_TIMINGS can be used, if it is set, then the hardware also supports timings that are not in that list. 5) It can be dangerous to allow userspace to set up random timings for an output as this can damage monitors. It depends on various factors whether or not this should be protected by requiring root access. This has to be signalled somehow. I think that we should add a flag to v4l2_enum_dv_timings that tells whether selecting that specific timing requires root permissions. And we also need a V4L2_DV_BT_CAP_CUSTOM_ROOT flag in struct v4l2_bt_timings_cap to signal whether setting up custom timings requires root permissions. 6) Parsing the timings structures can be difficult, and for many applications you are just interested in finding certain industry standard timings. This was the idea behind the original preset API, and I still think that that is very useful in practice. My general view is that the preset API should be deprecated and eventually removed. After extending the timings API I see no more need for the preset API. So that leaves the question how to incorporate the preset functionality in the timings API. I see two options: a) Add a preset or alias field to v4l2_enum_dv_timings. This just makes it easy for the application to check for specific formats and to store the timings. b) As a), but also add a new v4l2_dv_timings type: V4L2_DV_PRESET (or DV_ALIAS). This also has a struct v4l2_dv_preset (or dv_alias) that is used to store the preset value. This way you can set a preset directly using VIDIOC_S_DV_TIMINGS. Comments? Hans Verkuil -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
