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[85.228.174.190]) by smtp.gmail.com with ESMTPSA id i24sm719966lfg.83.2020.06.30.04.39.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Jun 2020 04:39:09 -0700 (PDT) Received: from johan by xi.terra with local (Exim 4.93.0.4) (envelope-from ) id 1jqEbS-0001Ec-TU; Tue, 30 Jun 2020 13:39:06 +0200 Date: Tue, 30 Jun 2020 13:39:06 +0200 From: Johan Hovold To: Michael Hanselmann Cc: Johan Hovold , linux-usb@vger.kernel.org, Michael Dreher , Jonathan Olds Subject: Re: [PATCH v2 6/6] USB: serial: ch341: Simulate break condition if not supported Message-ID: <20200630113906.GA3334@localhost> References: <91bacfa4097350b4731724f5820e06bc03e7e8f3.1585697281.git.public@hansmi.ch> <20200514144721.GG25962@localhost> <6e29707b-6774-9f25-25ac-4b4cd202a017@msgid.hansmi.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6e29707b-6774-9f25-25ac-4b4cd202a017@msgid.hansmi.ch> Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, May 28, 2020 at 12:21:11AM +0200, Michael Hanselmann wrote: > On 14.05.20 16:47, Johan Hovold wrote: > > On Tue, Mar 31, 2020 at 11:37:22PM +0000, Michael Hanselmann wrote: > >> static int ch341_set_baudrate_lcr(struct usb_device *dev, > >> - struct ch341_private *priv, u8 lcr) > >> + struct ch341_private *priv, > >> + unsigned baud_rate, u8 lcr) > > > > Use speed_t. > > Done. ch341_private.baud_rate and ch341_set_termios also use unsigned > though. Should those also be changed to speed_t? I'd just leave it for now. > >> + r = ch341_set_baudrate_lcr(port->serial->dev, priv, > >> + CH341_MIN_BPS, > >> + CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | > > > > Hmm. This would corrupt incoming data as well during the break. > > Yes, there's no way to avoid that. In my opinion being able to send a > break signal for a serial console interrupt (SysRq) outweighs the > corruption. Updated the comment on ch341_simulate_break to mention > the caveat. > > >> + dev_dbg(&port->dev, "%s - Leave break state requested\n", __func__); > >> + > >> + if (time_before(jiffies, priv->break_end)) { > >> + /* Wait until NUL byte is written */ > >> + delay = min_t(unsigned long, HZ, priv->break_end - jiffies); > > > > Looks like this can underflow if you're preempted after the check. > > Moved the subtraction before the min_t macro to only evaluate it once. That's not sufficient; the problem is that jiffies may be updated after time_before(). > >> + if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK) { > >> + dev_warn_once(&port->dev, > >> + "%s - hardware doesn't support real break" > >> + " condition, simulating instead\n", > >> + __func__); > > > > Don't break the string, and drop the __func__. > > Done, also for the other error messages you pointed out. > > Michael > > --- > From 94fec46e814276491c9a027c5d3912b68deb9c55 Mon Sep 17 00:00:00 2001 > From: Michael Hanselmann > Date: Thu, 5 Mar 2020 01:50:35 +0100 > Subject: [PATCH 2/2] USB: serial: ch341: Simulate break condition if not > supported > > A subset of all CH341 devices don't support a real break condition. This > fact is already used in the "ch341_detect_quirks" function. With this > change a quirk is implemented to simulate a break condition by > temporarily lowering the baud rate and sending a NUL byte. > > The primary drawbacks of this approach are that the duration of the > break can't be controlled by userland and that data incoming during > a simulated break is corrupted. > > The "TTY_DRIVER_HARDWARE_BREAK" serial driver flag was investigated as > an alternative. It's a driver-wide flag and would've required > significant changes to the serial and USB-serial driver frameworks to > expose it for individual USB-serial adapters. > > Tested by sending a break condition and watching the TX pin using an > oscilloscope. > > Signed-off-by: Michael Hanselmann > --- > drivers/usb/serial/ch341.c | 105 ++++++++++++++++++++++++++++++++++--- > 1 file changed, 97 insertions(+), 8 deletions(-) > > diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c > index 202cfa4ef6c7..1e63310cfd9c 100644 > --- a/drivers/usb/serial/ch341.c > +++ b/drivers/usb/serial/ch341.c > @@ -78,6 +78,7 @@ > #define CH341_LCR_CS5 0x00 > > #define CH341_QUIRK_LIMITED_PRESCALER BIT(0) > +#define CH341_QUIRK_SIMULATE_BREAK BIT(1) > > static const struct usb_device_id id_table[] = { > { USB_DEVICE(0x4348, 0x5523) }, > @@ -94,6 +95,7 @@ struct ch341_private { > u8 msr; > u8 lcr; > unsigned long quirks; > + unsigned long break_end; > }; > > static void ch341_set_termios(struct tty_struct *tty, > @@ -168,10 +170,9 @@ static const speed_t ch341_min_rates[] = { > * 2 <= div <= 256 if fact = 0, or > * 9 <= div <= 256 if fact = 1 > */ > -static int ch341_get_divisor(struct ch341_private *priv) > +static int ch341_get_divisor(struct ch341_private *priv, speed_t speed) > { > unsigned int fact, div, clk_div; > - speed_t speed = priv->baud_rate; > bool force_fact0 = false; > int ps; > > @@ -234,15 +235,16 @@ static int ch341_get_divisor(struct ch341_private *priv) > } > > static int ch341_set_baudrate_lcr(struct usb_device *dev, > - struct ch341_private *priv, u8 lcr) > + struct ch341_private *priv, > + speed_t baud_rate, u8 lcr) > { > int val; > int r; > > - if (!priv->baud_rate) > + if (!baud_rate) > return -EINVAL; > > - val = ch341_get_divisor(priv); > + val = ch341_get_divisor(priv, baud_rate); > if (val < 0) > return -EINVAL; > > @@ -322,7 +324,7 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv) > if (r < 0) > goto out; > > - r = ch341_set_baudrate_lcr(dev, priv, priv->lcr); > + r = ch341_set_baudrate_lcr(dev, priv, priv->baud_rate, priv->lcr); > if (r < 0) > goto out; > > @@ -356,7 +358,7 @@ static int ch341_detect_quirks(struct usb_serial_port *port) > CH341_REG_BREAK, 0, buffer, size, DEFAULT_TIMEOUT); > if (r == -EPIPE) { > dev_dbg(&port->dev, "break control not supported\n"); > - quirks = CH341_QUIRK_LIMITED_PRESCALER; > + quirks = CH341_QUIRK_LIMITED_PRESCALER | CH341_QUIRK_SIMULATE_BREAK; > r = 0; > goto out; > } > @@ -537,7 +539,8 @@ static void ch341_set_termios(struct tty_struct *tty, > if (baud_rate) { > priv->baud_rate = baud_rate; > > - r = ch341_set_baudrate_lcr(port->serial->dev, priv, lcr); > + r = ch341_set_baudrate_lcr(port->serial->dev, priv, > + priv->baud_rate, lcr); > if (r < 0 && old_termios) { > priv->baud_rate = tty_termios_baud_rate(old_termios); > tty_termios_copy_hw(&tty->termios, old_termios); > @@ -556,15 +559,101 @@ static void ch341_set_termios(struct tty_struct *tty, > ch341_set_handshake(port->serial->dev, priv->mcr); > } > > +/* > + * A subset of all CH34x devices don't support a real break condition and > + * reading CH341_REG_BREAK fails (see also ch341_detect_quirks). This function > + * simulates a break condition by lowering the baud rate to the minimum > + * supported by the hardware upon enabling the break condition and sending > + * a NUL byte. > + * > + * Incoming data is corrupted while the break condition is being simulated. > + * > + * Normally the duration of the break condition can be controlled individually > + * by userspace using TIOCSBRK and TIOCCBRK or by passing an argument to > + * TCSBRKP. Due to how the simulation is implemented the duration can't be > + * controlled. The duration is always about (1s / 46bd * 9bit) = 196ms. > + */ > +static void ch341_simulate_break(struct tty_struct *tty, int break_state) > +{ > + struct usb_serial_port *port = tty->driver_data; > + struct ch341_private *priv = usb_get_serial_port_data(port); > + unsigned long delay; > + int r; > + > + if (break_state != 0) { > + dev_dbg(&port->dev, "enter break state requested\n"); > + > + r = ch341_set_baudrate_lcr(port->serial->dev, priv, > + CH341_MIN_BPS, > + CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | > + CH341_LCR_CS8); Continuation lines should be indented at least two tabs further. And let's just merge the last two lines. > + if (r < 0) { > + dev_err(&port->dev, > + "failed to change baud rate to %u: %d\n", > + CH341_MIN_BPS, r); > + goto restore; > + } > + > + r = tty_put_char(tty, '\0'); > + if (r < 0) { > + dev_err(&port->dev, > + "failed to write NUL byte for simulated break condition: %d\n", > + r); > + goto restore; > + } > + > + /* > + * Compute how long transmission will take and add a bit of > + * safety margin. > + */ Where's that margin? > + priv->break_end = jiffies + (10 * HZ / CH341_MIN_BPS); > + > + return; > + } > + > + dev_dbg(&port->dev, "leave break state requested\n"); > + > + if (time_before(jiffies, priv->break_end)) { > + /* > + * Wait until NUL byte is written and limit delay to one second > + * at most. > + */ So you could still be preempted here so that delay would wrap. Just store jiffies in a "now" temporary before the conditional? > + delay = priv->break_end - jiffies; > + delay = min_t(unsigned long, HZ, delay); And then you can skip the min_t() here. > + > + dev_dbg(&port->dev, > + "wait %d ms while transmitting NUL byte at %u baud\n", > + jiffies_to_msecs(delay), CH341_MIN_BPS); > + schedule_timeout_interruptible(delay); > + } > + > +restore: > + /* Restore original baud rate */ > + r = ch341_set_baudrate_lcr(port->serial->dev, priv, priv->baud_rate, > + priv->lcr); > + if (r < 0) > + dev_err(&port->dev, > + "restoring original baud rate of %u failed: %d\n", > + priv->baud_rate, r); > +} > + > static void ch341_break_ctl(struct tty_struct *tty, int break_state) > { > const uint16_t ch341_break_reg = > ((uint16_t) CH341_REG_LCR << 8) | CH341_REG_BREAK; > struct usb_serial_port *port = tty->driver_data; > + struct ch341_private *priv = usb_get_serial_port_data(port); > int r; > uint16_t reg_contents; > uint8_t *break_reg; > > + if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK) { > + dev_warn_once(&port->dev, > + "hardware doesn't support real break condition, simulating instead\n"); This should probably be moved to probe and quirk_detect() and be a dev_info (e.g. consider having two of these devices in a system). > + ch341_simulate_break(tty, break_state); > + return; > + } > + > break_reg = kmalloc(2, GFP_KERNEL); > if (!break_reg) > return; Care to respin as a v4? Johan