linux-kernel - Re: [PATCH v3 2/2] serial: 8250: Add new 8250-core based Broadcom STB driver

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Date:   Fri, 12 Feb 2021 12:47:02 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Al Cooper <alcooperx@...il.com>, linux-kernel@...r.kernel.org
Cc:     bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-usb@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v3 2/2] serial: 8250: Add new 8250-core based Broadcom STB
 driver



On 2/12/2021 11:57 AM, Al Cooper wrote:
> Add a UART driver for the new Broadcom 8250 based STB UART. The new
> UART is backward compatible with the standard 8250, but has some
> additional features. The new features include a high accuracy baud
> rate clock system and DMA support.
> 
> The driver will use the new optional BAUD MUX clock to select the best
> one of the four master clocks (81MHz, 108MHz, 64MHz and 48MHz) to feed
> the baud rate selection logic for any requested baud rate.  This allows
> for more accurate BAUD rates when high speed baud rates are selected.
> 
> The driver will use the new UART DMA hardware if the UART DMA registers
> are specified in Device Tree "reg" property.
> 
> The driver also sets the UPSTAT_AUTOCTS flag when hardware flow control
> is enabled. This flag is needed for UARTs that don't assert a CTS
> changed interrupt when CTS changes and AFE (Hardware Flow Control) is
> enabled.
> 
> The driver also contains a workaround for a bug in the Synopsis 8250
> core. The problem is that at high baud rates, the RX partial FIFO
> timeout interrupt can occur but there is no RX data (DR not set in
> the LSR register). In this case the driver will not read the Receive
> Buffer Register, which clears the interrupt, and the system will get
> continuous UART interrupts until the next RX character arrives. The
> fix originally suggested by Synopsis was to read the Receive Buffer
> Register and discard the character when the DR bit in the LSR was
> not set, to clear the interrupt. The problem was that occasionally
> a character would arrive just after the DR bit check and a valid
> character would be discarded. The fix that was added will clear
> receive interrupts to stop the interrupt, deassert RTS to insure
> that no new data can arrive, wait for 1.5 character times for the
> sender to react to RTS and then check for data and either do a dummy
> read or a valid read. Sysfs error counters were also added and were
> used to help create test software that would cause the error condition.
> The counters can be found at:
> /sys/devices/platform/rdb/*serial/rx_bad_timeout_late_char
> /sys/devices/platform/rdb/*serial/rx_bad_timeout_no_char
> 
> Signed-off-by: Al Cooper <alcooperx@...il.com>
> ---
>  MAINTAINERS                            |    8 +
>  drivers/tty/serial/8250/8250_bcm7271.c | 1099 ++++++++++++++++++++++++
>  drivers/tty/serial/8250/Kconfig        |   11 +
>  drivers/tty/serial/8250/Makefile       |    1 +
>  drivers/tty/serial/8250/bcm7271_uart.h |  158 ++++
>  5 files changed, 1277 insertions(+)
>  create mode 100644 drivers/tty/serial/8250/8250_bcm7271.c
>  create mode 100644 drivers/tty/serial/8250/bcm7271_uart.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 64c7169db617..bb6ad2fc4376 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3582,6 +3582,14 @@ S:	Supported
>  F:	Documentation/devicetree/bindings/i2c/brcm,brcmstb-i2c.yaml
>  F:	drivers/i2c/busses/i2c-brcmstb.c
>  
> +BROADCOM BRCMSTB UART DRIVER
> +M:	Al Cooper <alcooperx@...il.com>
> +L:	linux-usb@...r.kernel.org

This should probably be linux-serial, copy pasted from the USB entry
down below presumably.
-- 
Florian