linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Pali Rohár" <pali@kernel.org>
To: Andrew Lunn <andrew@lunn.ch>
Cc: "Michael Turquette" <mturquette@baylibre.com>,
	"Stephen Boyd" <sboyd@kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Gregory Clement" <gregory.clement@bootlin.com>,
	"Sebastian Hesselbarth" <sebastian.hesselbarth@gmail.com>,
	"Vladimir Vid" <vladimir.vid@sartura.hr>,
	"Marek Behún" <kabel@kernel.org>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>,
	linux-clk@vger.kernel.org, linux-serial@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 2/5] serial: mvebu-uart: implement UART clock driver for configuring UART base clock
Date: Sat, 17 Jul 2021 20:05:40 +0200	[thread overview]
Message-ID: <20210717180540.ersg5bslik6ivjie@pali> (raw)
In-Reply-To: <YPMS24faTg9tqreR@lunn.ch>

On Saturday 17 July 2021 19:26:51 Andrew Lunn wrote:
> On Sat, Jul 17, 2021 at 02:38:26PM +0200, Pali Rohár wrote:
> > @@ -445,6 +472,7 @@ static void mvebu_uart_shutdown(struct uart_port *port)
> >  static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
> >  {
> >  	unsigned int d_divisor, m_divisor;
> > +	unsigned long flags;
> >  	u32 brdv, osamp;
> >  
> >  	if (!port->uartclk)
> > @@ -463,10 +491,12 @@ static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
> >  	m_divisor = OSAMP_DEFAULT_DIVISOR;
> >  	d_divisor = DIV_ROUND_CLOSEST(port->uartclk, baud * m_divisor);
> >  
> > +	spin_lock_irqsave(&mvebu_uart_lock, flags);
> 
> Hi Pali
> 
> You only need spin_lock_irqsave() if you plan on taking the spinlock
> in an interrupt handler. It seems unlikely the baud rate will be
> changed in interrupt context? Please check, and then swap to plain
> spin_lock().

Hello! Ok, I will check it.

> >  	brdv = readl(port->membase + UART_BRDV);
> >  	brdv &= ~BRDV_BAUD_MASK;
> >  	brdv |= d_divisor;
> >  	writel(brdv, port->membase + UART_BRDV);
> > +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
> >  
> >  	osamp = readl(port->membase + UART_OSAMP);
> >  	osamp &= ~OSAMP_DIVISORS_MASK;
> 
> > +	/* Recalculate UART1 divisor so UART1 baudrate does not change */
> > +	if (prev_clock_rate) {
> > +		divisor = DIV_U64_ROUND_CLOSEST((u64)(val & BRDV_BAUD_MASK) *
> > +						parent_clock_rate * prev_d1d2,
> > +						prev_clock_rate * d1 * d2);
> > +		if (divisor < 1)
> > +			divisor = 1;
> > +		else if (divisor > BRDV_BAUD_MAX)
> > +			divisor = BRDV_BAUD_MAX;
> > +		val = (val & ~BRDV_BAUD_MASK) | divisor;
> > +	}
> 
> I don't see any range checks in the patch which verifies the requested
> baud rate is actually possible. With code like this, it seems like the
> baud rate change will be successful, but the actual baud rate will not
> be what is requested.

This code is in function which changes parent UART clock from one used
by bootloader to clock which will be used by kernel UART driver.

Yes, it is possible if you configure something unusual in bootloader
that that this code breaks it. But I think there is not so much what we
can done here.

In other patches is updated function mvebu_uart_set_termios() which
verifies that you can set particular baudrate.

> > +	/* Recalculate UART2 divisor so UART2 baudrate does not change */
> > +	if (prev_clock_rate) {
> > +		val = readl(uart_clock_base->reg2);
> > +		divisor = DIV_U64_ROUND_CLOSEST((u64)(val & BRDV_BAUD_MASK) *
> > +						parent_clock_rate * prev_d1d2,
> > +						prev_clock_rate * d1 * d2);
> > +		if (divisor < 1)
> > +			divisor = 1;
> > +		else if (divisor > BRDV_BAUD_MAX)
> > +			divisor = BRDV_BAUD_MAX;
> > +		val = (val & ~BRDV_BAUD_MASK) | divisor;
> > +		writel(val, uart_clock_base->reg2);
> 
> Here it looks like UART1 could request a baud rate change, which ends
> up setting the clocks so that UART2 is out of range? Could the change
> for UART1 be successful, but you end up breaking UART2? I'm thinking
> when you are at opposite ends of the scale. UART2 is running at
> 110baud and UART1 at 230400baud.

This code is also in function which just do one time change of UART
parent clock. Once clk driver is probed this parent clock (and its d1
and d2 divisors) are not changed anymore. Parent clock and divisors are
chosen in way that kernel can always configure minimal baudrate 9600 on
both UARTs.

You are right that some combinations are not possible. But with these
patches it is fixed what is supported at clk driver probe time.

In v3 patch 5/5 is described how to calculate final baudrate from parent
clock and divisors d1, d2, d, m1, m2, m3, m4. Note that parent clock and
divisors d1 and d2 are shared for both UARTs. Other parameters (d, m1,
m2, m3, m4) can be set differently both UART1 and UART2. Changing shared
values is not possible during usage of UART.

If you have any idea how to improve current implementation, please let
me know.

Also note that all A3720 boards have disabled UART2 in DTS. And I'm not
sure if there is somebody who uses UART2 or who uses both UARTs.

  reply	other threads:[~2021-07-17 18:05 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-24 22:48 [PATCH 00/10] serial: mvebu-uart: Fixes and new support for higher baudrates Pali Rohár
2021-06-24 22:49 ` [PATCH 01/10] serial: mvebu-uart: fix calculation of clock divisor Pali Rohár
2021-06-24 22:49 ` [PATCH 02/10] serial: mvebu-uart: do not allow changing baudrate when uartclk is not available Pali Rohár
2021-06-24 22:49 ` [PATCH 03/10] serial: mvebu-uart: correctly calculate minimal possible baudrate Pali Rohár
2021-06-24 22:49 ` [PATCH 04/10] dt-bindings: mvebu-uart: fix documentation Pali Rohár
2021-06-24 22:49 ` [PATCH 05/10] arm64: dts: marvell: armada-37xx: Fix reg for standard variant of UART Pali Rohár
2021-06-24 22:49 ` [PATCH 06/10] serial: mvebu-uart: remove unused member nb from struct mvebu_uart Pali Rohár
2021-06-24 22:49 ` [PATCH 07/10] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár
2021-06-24 22:49 ` [PATCH 08/10] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár
2021-06-24 22:49 ` [PATCH 09/10] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár
2021-06-24 22:49 ` [PATCH 10/10] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár
2021-06-25 14:36 ` [PATCH v2 00/11] serial: mvebu-uart: Fixes and new support for higher baudrates Pali Rohár
2021-06-25 14:36   ` [PATCH v2 01/11] serial: mvebu-uart: fix calculation of clock divisor Pali Rohár
2021-06-25 14:36   ` [PATCH v2 02/11] serial: mvebu-uart: do not allow changing baudrate when uartclk is not available Pali Rohár
2021-06-25 14:36   ` [PATCH v2 03/11] serial: mvebu-uart: correctly calculate minimal possible baudrate Pali Rohár
2021-06-25 14:36   ` [PATCH v2 04/11] dt-bindings: mvebu-uart: fix documentation Pali Rohár
2021-06-25 14:36   ` [PATCH v2 05/11] arm64: dts: marvell: armada-37xx: Fix reg for standard variant of UART Pali Rohár
2021-06-25 14:36   ` [PATCH v2 06/11] serial: mvebu-uart: remove unused member nb from struct mvebu_uart Pali Rohár
2021-06-25 14:36   ` [PATCH v2 07/11] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár
2021-06-25 15:22     ` Geert Uytterhoeven
2021-06-25 15:38       ` Pali Rohár
2021-06-25 15:50         ` Willy Tarreau
2021-06-25 17:39           ` Geert Uytterhoeven
2021-06-25 17:44             ` Pali Rohár
2021-06-25 18:11               ` Geert Uytterhoeven
2021-07-19 12:45         ` Andy Shevchenko
2021-06-25 14:36   ` [PATCH v2 08/11] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár
2021-06-25 14:36   ` [PATCH v2 09/11] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár
2021-06-25 14:36   ` [PATCH v2 10/11] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár
2021-06-25 14:36   ` [PATCH v2 11/11] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár
2021-07-17 12:38 ` [PATCH v3 0/5] serial: mvebu-uart: Support for higher baudrates Pali Rohár
2021-07-17 12:38   ` [PATCH v3 1/5] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár
2021-07-19 12:47     ` Andy Shevchenko
2021-07-22 21:57       ` Pali Rohár
2021-07-24 11:38         ` David Laight
2021-07-17 12:38   ` [PATCH v3 2/5] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár
2021-07-17 17:26     ` Andrew Lunn
2021-07-17 18:05       ` Pali Rohár [this message]
2021-07-24  9:48         ` Pali Rohár
2021-07-24 16:33           ` Andrew Lunn
2021-07-25 12:14             ` Pali Rohár
2021-07-17 12:38   ` [PATCH v3 3/5] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár
2021-07-17 17:30     ` [PATCH v3 3/5] dt-bindings: mvebu-uart: document DT bindings for marvell, armada-3700-uart-clock Andrew Lunn
2021-08-02 14:45       ` Pali Rohár
2021-07-17 12:38   ` [PATCH v3 4/5] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár
2021-07-17 12:38   ` [PATCH v3 5/5] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár
2021-08-02 14:45 ` [PATCH v4 0/6] serial: mvebu-uart: Support for higher baudrates Pali Rohár
2021-08-02 14:45   ` [PATCH v4 1/6] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár
2021-08-02 14:45   ` [PATCH v4 2/6] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár
2021-08-02 14:45   ` [PATCH v4 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár
2021-08-06  0:30     ` Stephen Boyd
2021-08-06  8:28       ` Pali Rohár
2021-08-12 19:33         ` Stephen Boyd
2021-08-12 20:08           ` Pali Rohár
2021-08-02 14:45   ` [PATCH v4 4/6] dt-bindings: mvebu-uart: update information about UART clock Pali Rohár
2021-08-02 14:45   ` [PATCH v4 5/6] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár
2021-08-02 14:45   ` [PATCH v4 6/6] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár
2021-08-09 14:53 ` [PATCH v5 0/6] serial: mvebu-uart: Support for higher baudrates Pali Rohár
2021-08-09 14:53   ` [PATCH v5 1/6] math64: New DIV_U64_ROUND_CLOSEST helper Pali Rohár
2021-08-09 14:53   ` [PATCH v5 2/6] serial: mvebu-uart: implement UART clock driver for configuring UART base clock Pali Rohár
2021-08-09 14:53   ` [PATCH v5 3/6] dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock Pali Rohár
2021-08-09 14:53   ` [PATCH v5 4/6] dt-bindings: mvebu-uart: update information about UART clock Pali Rohár
2021-08-09 14:53   ` [PATCH v5 5/6] arm64: dts: marvell: armada-37xx: add device node for UART clock and use it Pali Rohár
2021-08-09 14:53   ` [PATCH v5 6/6] serial: mvebu-uart: implement support for baudrates higher than 230400 Pali Rohár
2021-08-20 17:22   ` [PATCH v5 0/6] serial: mvebu-uart: Support for higher baudrates Pali Rohár
2021-08-31  8:35     ` Pali Rohár
2021-09-21  7:41       ` Greg Kroah-Hartman

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210717180540.ersg5bslik6ivjie@pali \
    --to=pali@kernel.org \
    --cc=andrew@lunn.ch \
    --cc=geert@linux-m68k.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=gregory.clement@bootlin.com \
    --cc=kabel@kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-clk@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-serial@vger.kernel.org \
    --cc=mturquette@baylibre.com \
    --cc=robh+dt@kernel.org \
    --cc=sboyd@kernel.org \
    --cc=sebastian.hesselbarth@gmail.com \
    --cc=vladimir.vid@sartura.hr \
    --subject='Re: [PATCH v3 2/5] serial: mvebu-uart: implement UART clock driver for configuring UART base clock' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).