From: Zev Weiss <zev@bewilderbeest.net>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-aspeed@lists.ozlabs.org,
Konstantin Aladyshev <aladyshev22@gmail.com>,
Andrew Jeffery <andrew@aj.id.au>,
openbmc@lists.ozlabs.org, linux-kernel@vger.kernel.org,
Oskar Senft <osk@google.com>,
linux-serial@vger.kernel.org,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Jiri Slaby <jirislaby@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type
Date: Thu, 10 Feb 2022 01:22:09 -0800 [thread overview]
Message-ID: <YgTZQQuTkLjnkeyB@hatter.bewilderbeest.net> (raw)
In-Reply-To: <YgTKvIqTIOomFSsF@kroah.com>
On Thu, Feb 10, 2022 at 12:20:12AM PST, Greg Kroah-Hartman wrote:
>On Wed, Feb 09, 2022 at 11:49:47PM -0800, Zev Weiss wrote:
>> On Wed, Feb 09, 2022 at 11:40:42PM PST, Greg Kroah-Hartman wrote:
>> > On Wed, Feb 09, 2022 at 12:34:14PM -0800, Zev Weiss wrote:
>> > > Commit 54da3e381c2b ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to
>> > > set up register mapping") fixed a bug that had, as a side-effect,
>> > > prevented the 8250_aspeed_vuart driver from enabling the VUART's
>> > > FIFOs. However, fixing that (and hence enabling the FIFOs) has in
>> > > turn revealed what appears to be a hardware bug in the ASPEED VUART in
>> > > which the host-side THRE bit doesn't get if the BMC-side receive FIFO
>> > > trigger level is set to anything but one byte. This causes problems
>> > > for polled-mode writes from the host -- for example, Linux kernel
>> > > console writes proceed at a glacial pace (less than 100 bytes per
>> > > second) because the write path waits for a 10ms timeout to expire
>> > > after every character instead of being able to continue on to the next
>> > > character upon seeing THRE asserted. (GRUB behaves similarly.)
>> > >
>> > > As a workaround, introduce a new port type for the ASPEED VUART that's
>> > > identical to PORT_16550A as it had previously been using, but with
>> > > UART_FCR_R_TRIG_00 instead to set the receive FIFO trigger level to
>> > > one byte, which (experimentally) seems to avoid the problematic THRE
>> > > behavior.
>> > >
>> > > Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
>> > > Tested-by: Konstantin Aladyshev <aladyshev22@gmail.com>
>> >
>> > Do we need a "Fixes:" tag here as well?
>>
>> I was wondering the same -- I left it out because it didn't seem like it was
>> strictly a bug in the earlier commit that's really being fixed per se, but
>> perhaps that's an overly pedantic distinction. I can certainly add it if
>> you'd prefer.
>
>This obviously fixes an issue, if you don't have a specific commit that
>caused it, a cc: stable@vger.kernel.org should be added so we know to
>backport this to all stable kernels.
>
Okay -- well, I suppose it's a fix in the sense that if you have the
earlier commit, you'll also want this one, so I'll add the tag.
>>
>> >
>> > > ---
>> > > drivers/tty/serial/8250/8250_aspeed_vuart.c | 2 +-
>> > > drivers/tty/serial/8250/8250_port.c | 8 ++++++++
>> > > include/uapi/linux/serial_core.h | 3 +++
>> > > 3 files changed, 12 insertions(+), 1 deletion(-)
>> > >
>> > > diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c
>> > > index 2350fb3bb5e4..c2cecc6f47db 100644
>> > > --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c
>> > > +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c
>> > > @@ -487,7 +487,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev)
>> > > port.port.irq = irq_of_parse_and_map(np, 0);
>> > > port.port.handle_irq = aspeed_vuart_handle_irq;
>> > > port.port.iotype = UPIO_MEM;
>> > > - port.port.type = PORT_16550A;
>> > > + port.port.type = PORT_ASPEED_VUART;
>> > > port.port.uartclk = clk;
>> > > port.port.flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP
>> > > | UPF_FIXED_PORT | UPF_FIXED_TYPE | UPF_NO_THRE_TEST;
>> > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
>> > > index 3b12bfc1ed67..973870ebff69 100644
>> > > --- a/drivers/tty/serial/8250/8250_port.c
>> > > +++ b/drivers/tty/serial/8250/8250_port.c
>> > > @@ -307,6 +307,14 @@ static const struct serial8250_config uart_config[] = {
>> > > .rxtrig_bytes = {1, 32, 64, 112},
>> > > .flags = UART_CAP_FIFO | UART_CAP_SLEEP,
>> > > },
>> > > + [PORT_ASPEED_VUART] = {
>> > > + .name = "ASPEED VUART",
>> > > + .fifo_size = 16,
>> > > + .tx_loadsz = 16,
>> > > + .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00,
>> > > + .rxtrig_bytes = {1, 4, 8, 14},
>> > > + .flags = UART_CAP_FIFO,
>> > > + },
>> > > };
>> > >
>> > > /* Uart divisor latch read */
>> > > diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
>> > > index c4042dcfdc0c..cd11748833e6 100644
>> > > --- a/include/uapi/linux/serial_core.h
>> > > +++ b/include/uapi/linux/serial_core.h
>> > > @@ -274,4 +274,7 @@
>> > > /* Freescale LINFlexD UART */
>> > > #define PORT_LINFLEXUART 122
>> > >
>> > > +/* ASPEED AST2x00 virtual UART */
>> > > +#define PORT_ASPEED_VUART 123
>> >
>> > Why does this value have to be in a uapi header file? What userspace
>> > tool is going to need this?
>> >
>>
>> I only put it there because that was where all the other port type constants
>> were defined, and wondered the same thing about the lot of them. Is there a
>> userspace tool that makes use of any of these?
>
>Not really, please don't add it if you do not require it.
>
It seems like an odd inconsistency to put this one particular definition
somewhere else when the other 100+ of its siblings are in the uapi
header; would you want a preceding patch to move them all somewhere
under include/linux? (Which in turn doesn't really seem like a change
for -stable I'd think.)
Though actually, on further investigation I see those constants are in
fact exposed to userspace in struct serial_struct->type (via
TIOCGSERIAL/TIOCSSERIAL), and via the 'type' sysfs attribute, so I'd
think we'd probably want to keep them as they are?
Zev
next prev parent reply other threads:[~2022-02-10 9:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-09 20:34 [PATCH] serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type Zev Weiss
2022-02-10 7:40 ` Greg Kroah-Hartman
2022-02-10 7:49 ` Zev Weiss
2022-02-10 8:20 ` Greg Kroah-Hartman
2022-02-10 9:22 ` Zev Weiss [this message]
2022-02-10 10:46 ` Greg Kroah-Hartman
2022-02-10 11:11 ` Andy Shevchenko
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=YgTZQQuTkLjnkeyB@hatter.bewilderbeest.net \
--to=zev@bewilderbeest.net \
--cc=aladyshev22@gmail.com \
--cc=andrew@aj.id.au \
--cc=andriy.shevchenko@linux.intel.com \
--cc=gregkh@linuxfoundation.org \
--cc=jirislaby@kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-aspeed@lists.ozlabs.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-serial@vger.kernel.org \
--cc=openbmc@lists.ozlabs.org \
--cc=osk@google.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).