From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 89FA4FBF0; Thu, 7 Nov 2024 08:47:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730969245; cv=none; b=QbWcDJYkeqVNyb1VSNJGyrlDYkDjKiwc2HpLIh6lWqxwOea3kROo+rUS7lbNv/PM6XPzA2exaAyKxFNTX7gmXL+o9OBgEa48P7slPSan+GL+ZGWoeprGHnd9U+GZbyrRytC1cpjHLF48t0lhXFyxj+0D2DSjuGoWcqy5wRuaDK4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730969245; c=relaxed/simple; bh=9/KGz9Eqf8L6AckABuzu+EnLUD9DwMieaH9zCgdF3uY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=tOflHzBPrHCpSpaivq6D4nBwfIh8CHiJf8eSNJdZ1XayXyLQI8vGlYnQI67xd+vnOX6xNYBy3ZxJbtVf/Wc+QVTkpvtQe07yCu8xTNOrfg/jjyYplOy9BY/zLE77ZQ+m58t9K0xBF7sqPU321LWg5l6vKNITKbu1ZT93AzEz0mQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=iEyYs2Nz; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="iEyYs2Nz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5117C4CECC; Thu, 7 Nov 2024 08:47:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1730969245; bh=9/KGz9Eqf8L6AckABuzu+EnLUD9DwMieaH9zCgdF3uY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=iEyYs2NzyAXwOllRBBtt61ypuqxImxlWvXnXclkI+SY0H11AsXGNwgA4M28QqrGx1 cTP6PdDqgbXb/ad96I9TiWi4/nFjzo245/xxRb1HYzvT8a20x0obqGnSVnu4vgrPdT WUqBeuazkGU+kk8ysYcvbheWdPOl/e7uyTJxviJg= Date: Thu, 7 Nov 2024 09:47:05 +0100 From: Greg KH To: Claudiu Cc: geert+renesas@glider.be, magnus.damm@gmail.com, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, mturquette@baylibre.com, sboyd@kernel.org, jirislaby@kernel.org, p.zabel@pengutronix.de, lethal@linux-sh.org, g.liakhovetski@gmx.de, ysato@users.sourceforge.jp, ulrich.hecht+renesas@gmail.com, linux-renesas-soc@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org, linux-serial@vger.kernel.org, Claudiu Beznea , stable@vger.kernel.org Subject: Re: [PATCH 2/9] serial: sh-sci: Check if TX data was written to device in .tx_empty() Message-ID: <2024110747-kite-pacemaker-6216@gregkh> References: <20241106120118.1719888-1-claudiu.beznea.uj@bp.renesas.com> <20241106120118.1719888-3-claudiu.beznea.uj@bp.renesas.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241106120118.1719888-3-claudiu.beznea.uj@bp.renesas.com> On Wed, Nov 06, 2024 at 02:01:11PM +0200, Claudiu wrote: > From: Claudiu Beznea > > On the Renesas RZ/G3S, when doing suspend to RAM, the uart_suspend_port() > is called. The uart_suspend_port() calls 3 times the > struct uart_port::ops::tx_empty() before shutting down the port. > > According to the documentation, the struct uart_port::ops::tx_empty() > API tests whether the transmitter FIFO and shifter for the port is > empty. > > The Renesas RZ/G3S SCIFA IP reports the number of data units stored in the > transmit FIFO through the FDR (FIFO Data Count Register). The data units > in the FIFOs are written in the shift register and transmitted from there. > The TEND bit in the Serial Status Register reports if the data was > transmitted from the shift register. > > In the previous code, in the tx_empty() API implemented by the sh-sci > driver, it is considered that the TX is empty if the hardware reports the > TEND bit set and the number of data units in the FIFO is zero. > > According to the HW manual, the TEND bit has the following meaning: > > 0: Transmission is in the waiting state or in progress. > 1: Transmission is completed. > > It has been noticed that when opening the serial device w/o using it and > then switch to a power saving mode, the tx_empty() call in the > uart_port_suspend() function fails, leading to the "Unable to drain > transmitter" message being printed on the console. This is because the > TEND=0 if nothing has been transmitted and the FIFOs are empty. As the > TEND=0 has double meaning (waiting state, in progress) we can't > determined the scenario described above. > > Add a software workaround for this. This sets a variable if any data has > been sent on the serial console (when using PIO) or if the DMA callback has > been called (meaning something has been transmitted). > > Fixes: 73a19e4c0301 ("serial: sh-sci: Add DMA support.") > Cc: stable@vger.kernel.org > Signed-off-by: Claudiu Beznea > --- > drivers/tty/serial/sh-sci.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c > index df523c744423..8e2d534401fa 100644 > --- a/drivers/tty/serial/sh-sci.c > +++ b/drivers/tty/serial/sh-sci.c > @@ -153,6 +153,7 @@ struct sci_port { > int rx_trigger; > struct timer_list rx_fifo_timer; > int rx_fifo_timeout; > + atomic_t first_time_tx; Don't use an atomic variable for an informational thing like this, it is racy and doesn't work properly. Either use a real lock (because you care about the locking stuff here), or just use a boolean and live with any potential races. > u16 hscif_tot; > > bool has_rtscts; > @@ -850,6 +851,7 @@ static void sci_transmit_chars(struct uart_port *port) > { > struct tty_port *tport = &port->state->port; > unsigned int stopped = uart_tx_stopped(port); > + struct sci_port *s = to_sci_port(port); > unsigned short status; > unsigned short ctrl; > int count; > @@ -885,6 +887,7 @@ static void sci_transmit_chars(struct uart_port *port) > } > > sci_serial_out(port, SCxTDR, c); > + atomic_set(&s->first_time_tx, 1); > > port->icount.tx++; > } while (--count > 0); > @@ -1241,6 +1244,8 @@ static void sci_dma_tx_complete(void *arg) > if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS) > uart_write_wakeup(port); > > + atomic_set(&s->first_time_tx, 1); > + > if (!kfifo_is_empty(&tport->xmit_fifo)) { > s->cookie_tx = 0; > schedule_work(&s->work_tx); > @@ -2076,6 +2081,10 @@ static unsigned int sci_tx_empty(struct uart_port *port) > { > unsigned short status = sci_serial_in(port, SCxSR); > unsigned short in_tx_fifo = sci_txfill(port); > + struct sci_port *s = to_sci_port(port); > + > + if (!atomic_read(&s->first_time_tx)) > + return TIOCSER_TEMT; See, what happens here if the value changes right after you check it? Being an atomic doesn't mean anything :( thanks, greg k-h