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Sat, 18 Apr 2026 20:27:11 -0700 (PDT) Received: from arch.localdomain ([103.182.132.254]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b5fab0cf3bsm74202655ad.44.2026.04.18.20.27.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 18 Apr 2026 20:27:11 -0700 (PDT) From: Debjeet Banerjee To: dtwlin@gmail.com Cc: johan@kernel.org, elder@kernel.org, gregkh@linuxfoundation.org, greybus-dev@lists.linaro.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, debjeetbanerjee48@gmail.com Subject: [PATCH] staging: greybus: uart: document c_cflag handling in set_termios Date: Sun, 19 Apr 2026 08:56:32 +0530 Message-ID: <20260419032632.35351-1-debjeetbanerjee48@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit gb_tty_set_termios() derives UART line configuration from a subset of termios->c_cflag bits, namely CSIZE, CSTOPB, PARENB, PARODD, CMSPAR, CRTSCTS, CLOCAL and CBAUD. Other c_cflag bits are not interpreted by the driver and are not represented in the Greybus UART protocol messages. The existing FIXME suggests clearing unsupported bits from termios. However, the driver already limits its behavior to the supported subset when constructing line coding, and unused bits are effectively ignored. No invalid or unsupported values are propagated to the hardware. Replace the FIXME with a comment documenting which c_cflag bits are consumed by the driver and clarifying that other bits are ignored. No functional change intended. Signed-off-by: Debjeet Banerjee --- drivers/staging/greybus/uart.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/staging/greybus/uart.c b/drivers/staging/greybus/uart.c index 7d060b4cd33d..49d685a6ad8c 100644 --- a/drivers/staging/greybus/uart.c +++ b/drivers/staging/greybus/uart.c @@ -494,8 +494,20 @@ static void gb_tty_set_termios(struct tty_struct *tty, (termios->c_cflag & CMSPAR ? 2 : 0) : 0; newline.data_bits = tty_get_char_size(termios->c_cflag); - - /* FIXME: needs to clear unsupported bits in the termios */ + /* + * The Greybus UART driver only interprets a subset of termios + * c_cflag bits when configuring line settings: + * + * - CSIZE via tty_get_char_size() for data bits + * - CSTOPB for stop-bit format + * - PARENB, PARODD, CMSPAR for parity encoding + * - CRTSCTS for hardware flow control + * - CLOCAL for modem control handling + * - CBAUD via C_BAUD() for baud rate and B0 semantics + * + * Other c_cflag bits are ignored as they are not represented in + * the Greybus UART protocol. + */ gb_tty->clocal = ((termios->c_cflag & CLOCAL) != 0); if (C_BAUD(tty) == B0) { -- 2.53.0