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Commitb8e0ddd36c("can: mcp251xfd: tef: prepare to workaround broken TEF FIFO tail index erratum") introduced mcp251xfd_get_tef_len() to get the number of unhandled transmit events from the Transmit Event FIFO (TEF). As the TEF has no head pointer, the driver uses the TX FIFO's tail pointer instead, assuming that send frames are completed. However the check for the TEF being full was not correct. This leads to the driver stop working if the TEF is full. Fix the TEF full check by assuming that if, from the driver's point of view, there are no free TX buffers in the chip and the TX FIFO is empty, all messages must have been sent and the TEF must therefore be full. Reported-by: Sven Schuchmann <schuchmann@schleissheimer.de> Closes: https://patch.msgid.link/FR3P281MB155216711EFF900AD9791B7ED9692@FR3P281MB1552.DEUP281.PROD.OUTLOOK.COM Fixes:b8e0ddd36c("can: mcp251xfd: tef: prepare to workaround broken TEF FIFO tail index erratum") Tested-by: Sven Schuchmann <schuchmann@schleissheimer.de> Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20241104-mcp251xfd-fix-length-calculation-v3-1-608b6e7e2197@pengutronix.de Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>