From be627f257ce283c95fd2988080dc0db3a20d0d2a Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Fri, 10 Jul 2026 11:53:17 +0200 Subject: [PATCH] media: cec: tegra_cec: don't break off msg on NACK The Tegra CEC hardware has a bug where, if the first attempt to transmit a message is NACKed so the transmit is aborted, then the second attempt can contain corrupt data. Ensure that the full message is always transmitted to avoid hitting this bug. I suspect some internal state is not reset in the case of aborting a message due to a NACK. Signed-off-by: Hans Verkuil Reviewed-by: Mikko Perttunen Signed-off-by: Mauro Carvalho Chehab --- drivers/media/cec/platform/tegra/tegra_cec.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/media/cec/platform/tegra/tegra_cec.c b/drivers/media/cec/platform/tegra/tegra_cec.c index fe66336e734f..f8ffaeb78118 100644 --- a/drivers/media/cec/platform/tegra/tegra_cec.c +++ b/drivers/media/cec/platform/tegra/tegra_cec.c @@ -243,7 +243,18 @@ static int tegra_cec_adap_enable(struct cec_adapter *adap, bool enable) TEGRA_CEC_INT_MASK_RX_REGISTER_FULL | TEGRA_CEC_INT_MASK_RX_START_BIT_DETECTED); - cec_write(cec, TEGRA_CEC_HW_CONTROL, TEGRA_CEC_HWCTRL_TX_RX_MODE); + /* + * TX_NAK_MODE ensures that the whole message is transmitted even + * if each byte is NACKed. Without this flag the retransmit of the + * messages after a NACK can be corrupt. This is a bug in the hardware. + * + * While less efficient, in practice you rarely transmit messages + * that can be NACKed, with the exception of POLL messages which + * are just one byte anyway. + */ + cec_write(cec, TEGRA_CEC_HW_CONTROL, + TEGRA_CEC_HWCTRL_TX_RX_MODE | + TEGRA_CEC_HWCTRL_TX_NAK_MODE); return 0; }