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This is again a big rewrite of the driver; now it touches the code to process PCM stream transfers. The most fundamental change is that the driver may support more than four periods. Instead of keeping the same index between both the ring buffer (with the fixed four buffer descriptors) and the PCM buffer periods, we keep difference indices for both (bd_head and pcm_head fields). In addition, when the periods are more than four, we need to track both head and next indices. That is, we now have three indices: bd_head, pcm_head and pcm_filled. Also, the driver works better for periods < 4, too: the remaining BDs out of four are marked as invalid, so that the hardware skips those BDs in its loop. By this flexibility, we can use even ALSA-lib dmix plugin, which requires 16 periods as default. The buffer size could be up to 20bit, so the max buffer size was increased accordingly. However, the buffer pre-allocation is kept as the old value (600kB) as default. The reason is the limited number of BDs: since it doesn't suffice for the useful SG page management that can fit with the usual page allocator like some other drivers, we have to still allocate continuous pages, hence we shouldn't take too big memories there. Signed-off-by: Takashi Iwai <tiwai@suse.de>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.