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A possible hardware bug was discovered when using CA addon hardware attached to the ngene hardware, in that the TS input buffer much likely will shift and thus become unaligned to 188 byte blocks (a full TS frame) when things like CA module initialisation (which happens via differing communication paths) take place. This causes the TS NULL removal in tsin_exchange() to fail to detect this previously inserted data and thus causes userspace applications to receive data they didn't sent beforehand and ultimately cause troubles. On driver load with an inserted CAM, buffers are fine at first (note that the driver has to keep the communication running from/to the card by inserting TS NULL frames, this is done in tsout_exchange() via FillTSBuffer() - that data is simply sent back by the hardware): offset | 0 1 2 3 4 5 .... 188 189 190 191 192 193 .... 376 data | 47 1f ff 10 6f 6f .... 47 1f ff 10 6f 6f .... 47 After a few seconds, the CA module is recognised and initialised, which is signalled by dvb_ca_en50221: dvb_ca adapter X: DVB CAM detected and initialised successfully This is where the first shift happens (this is always four bytes), buffer becomes like this: offset | 0 1 2 3 4 5 .... 188 189 190 191 192 193 .... 376 data | 6f 6f 6f 6f 47 1f .... 6f 6f 6f 6f 47 1f .... 6f Next, VDR, TVHeadend or any other CI aware application is started, buffers will shift by even more bytes. It is believed this is due to the hardware not handling control and data bytes properly distinct, and control data having an influence on the actual data stream, which we cannot properly detect at the driver level. Workaround this hardware quirk by adding a detection for the TS sync byte 0x47 before each TS frame copy, scan for a new SYNC byte and a TS NULL packet if buffers become unaligned, take note of that offset and apply that when copying data to the DVB ring buffers. The last <188 bytes from the hardware buffers are stored in a temp buffer (tsin_buffer), for which the remainder will be in the beginning of the next hardware buffer (next iteration of tsin_exchange()). That remainder will be appended to the temp buffer and finally sent to the DVB ring buffer. The resulting TS stream is perfectly fine, and the TS NULL packets inserted by the driver which are sent back are properly removed. The resulting offset is being clamped to 188 byte segments (one TS packet). Though this can result in a repeated TS packet if the overall offset grows beyond this (and it will grow only on CA initialisation), this is still way better than unaligned TS frames and data sent to userspace that just isn't supposed to be there. This compensation can be toggled by the ci_tsfix modparam, which defaults to 1 (enabled). In the case of problems, this can be turned off by setting the parameter to 0 to restore the old behaviour. Signed-off-by: Daniel Scheller <d.scheller@gmx.net> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> |
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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.