Messages in this thread | | | Subject | Re: [Xen-devel] [RFC v1] ALSA: xen-front: Add Xen para-virtualized frontend driver | From | Oleksandr Andrushchenko <> | Date | Mon, 11 Dec 2017 10:45:27 +0200 |
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ping
On 11/17/2017 10:08 AM, Oleksandr Andrushchenko wrote: > ping > > On 11/02/2017 03:11 PM, Oleksandr Andrushchenko wrote: >> Hi, all! >> >> Foreword >> ======== >> >> This RFC is aimed to introduce support of para-virtualized sound >> frontend >> driver for Xen [1] and gather opinions from the relevant communities >> (ALSA, Xen). It implements the protocol from [2] with the >> following limitations: >> - mute/unmute is not supported >> - get/set volume is not supported >> Volume control is not supported for the reason that most of the >> use-cases >> (at the moment) are based on scenarios where unprivileged OS >> (e.g. Android, AGL etc) uses software mixers. >> Both capture and playback are supported. >> >> The relevant backend is implemented as a user-space application [3] >> and uses accompanying helper library [4]. >> >> Both frontend driver and backend were tested on real HW running Xen >> hypervisor >> (Renesas R-Car ARM based H3/M3 boards, x86). >> >> Discussion >> ========== >> >> During the first attempt to upstream the driver [5] number of >> comments and >> concerns were raised, one of the biggest flaws in the design were >> questioned >> by both Clemens Ladisch [6] and Takashi Sakamoto [7]: the absence of >> synchronization between frontend and backend during capture/playback. >> Two options were discussed: >> >> “In design of ALSA PCM core, drivers are expected to synchronize to >> actual hardwares for semi-realtime data transmission. The >> synchronization is done by two points: >> 1) Interrupts to respond events from actual hardwares. >> 2) Positions of actual data transmission in any serial sound interfaces >> of actual hardwares. >> “ >> >> and finally a change to the existing protocol was suggested: >> >> “In 'include/xen/interface/io/sndif.h', there's no functionalities I >> described the above: >> 1. notifications from DomU to Dom0 about the size of period for >> interrupts from actual hardwares. Or no way from Dom0 to DomU about >> the configured size of the period. >> 2. notifications of the interrupts from actual hardwares to DomU.” >> >> This is implemented as a change to the sndif protocol [8] and allows >> removing >> period emulation: >> 1. Introduced a new event channel from back to front >> 2. New event with number of bytes played/captured (XENSND_EVT_CUR_POS, >> to be used for sending snd_pcm_period_elapsed at frontend (in Linux >> implementation). Sent in bytes, not frames to make the protocol >> generic and consistent) >> 3. New request for playback/capture control (XENSND_OP_TRIGGER) with >> start/pause/stop/resume sub-ops. >> >> Along with these changes other comments on the driver were addressed, >> e.g. split into smaller chunks, moved the driver from misc to xen etc. >> >> >> Hope, this helps to get the full picture of what was discussed and >> makes it >> possible to move forward. >> >> Waiting for your valuable comments, >> >> Thank you, >> Oleksandr >> >> [1] https://github.com/andr2000/linux/commits/snd_upstream_v1 >> [2] >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/xen/interface/io/sndif.h >> [3] https://github.com/xen-troops/snd_be >> [4] https://github.com/xen-troops/libxenbe >> [5] https://lkml.org/lkml/2017/8/7/363 >> [6] >> http://mailman.alsa-project.org/pipermail/alsa-devel/2017-August/123617.html >> [7] >> http://mailman.alsa-project.org/pipermail/alsa-devel/2017-August/123744.html >> [8] >> https://github.com/andr2000/linux/commit/095d7feae00bf00c852c67c4f1044de5601678ed >> >> >> >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@lists.xen.org >> https://lists.xen.org/xen-devel >
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