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Diffstat (limited to 'Documentation/video4linux/bttv/README.quirks')
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diff --git a/Documentation/video4linux/bttv/README.quirks b/Documentation/video4linux/bttv/README.quirks deleted file mode 100644 index 92e03929a..000000000 --- a/Documentation/video4linux/bttv/README.quirks +++ /dev/null @@ -1,83 +0,0 @@ - -Below is what the bt878 data book says about the PCI bug compatibility -modes of the bt878 chip. - -The triton1 insmod option sets the EN_TBFX bit in the control register. -The vsfx insmod option does the same for EN_VSFX bit. If you have -stability problems you can try if one of these options makes your box -work solid. - -drivers/pci/quirks.c knows about these issues, this way these bits are -enabled automagically for known-buggy chipsets (look at the kernel -messages, bttv tells you). - -HTH, - - Gerd - ----------------------------- cut here -------------------------- - -Normal PCI Mode ---------------- - -The PCI REQ signal is the logical-or of the incoming function requests. -The inter-nal GNT[0:1] signals are gated asynchronously with GNT and -demultiplexed by the audio request signal. Thus the arbiter defaults to -the video function at power-up and parks there during no requests for -bus access. This is desirable since the video will request the bus more -often. However, the audio will have highest bus access priority. Thus -the audio will have first access to the bus even when issuing a request -after the video request but before the PCI external arbiter has granted -access to the Bt879. Neither function can preempt the other once on the -bus. The duration to empty the entire video PCI FIFO onto the PCI bus is -very short compared to the bus access latency the audio PCI FIFO can -tolerate. - - -430FX Compatibility Mode ------------------------- - -When using the 430FX PCI, the following rules will ensure -compatibility: - - (1) Deassert REQ at the same time as asserting FRAME. - (2) Do not reassert REQ to request another bus transaction until after - finish-ing the previous transaction. - -Since the individual bus masters do not have direct control of REQ, a -simple logical-or of video and audio requests would violate the rules. -Thus, both the arbiter and the initiator contain 430FX compatibility -mode logic. To enable 430FX mode, set the EN_TBFX bit as indicated in -Device Control Register on page 104. - -When EN_TBFX is enabled, the arbiter ensures that the two compatibility -rules are satisfied. Before GNT is asserted by the PCI arbiter, this -internal arbiter may still logical-or the two requests. However, once -the GNT is issued, this arbiter must lock in its decision and now route -only the granted request to the REQ pin. The arbiter decision lock -happens regardless of the state of FRAME because it does not know when -FRAME will be asserted (typically - each initiator will assert FRAME on -the cycle following GNT). When FRAME is asserted, it is the initiator s -responsibility to remove its request at the same time. It is the -arbiters responsibility to allow this request to flow through to REQ and -not allow the other request to hold REQ asserted. The decision lock may -be removed at the end of the transaction: for example, when the bus is -idle (FRAME and IRDY). The arbiter decision may then continue -asynchronously until GNT is again asserted. - - -Interfacing with Non-PCI 2.1 Compliant Core Logic -------------------------------------------------- - -A small percentage of core logic devices may start a bus transaction -during the same cycle that GNT is de-asserted. This is non PCI 2.1 -compliant. To ensure compatibility when using PCs with these PCI -controllers, the EN_VSFX bit must be enabled (refer to Device Control -Register on page 104). When in this mode, the arbiter does not pass GNT -to the internal functions unless REQ is asserted. This prevents a bus -transaction from starting the same cycle as GNT is de-asserted. This -also has the side effect of not being able to take advantage of bus -parking, thus lowering arbitration performance. The Bt879 drivers must -query for these non-compliant devices, and set the EN_VSFX bit only if -required. - |