[RFC] serial: pl01x: add sbsa-uart favor

AKASHI Takahiro takahiro.akashi at linaro.org
Thu Nov 5 10:46:00 CET 2020 

Hi Oleksandr,

On Thu, Nov 05, 2020 at 09:18:39AM +0000, Oleksandr Andrushchenko wrote:
> Hello,
> 
> On 11/4/20 7:24 AM, AKASHI Takahiro wrote:
> > sbsa-uart is a virtual UART device with a sub-set of PL011 functionality
> > which is described in SBSA (Server Base System Architecture)[1].
> >
> > It mainly targets for server use, but sbsa-uart itself is useful in any
> > para-virtualized use cases, including Xen.
> >
> > At present, this patch is submitted as RFC because:
> > * for some reason, data cache must be turned off (in initr_dcache())
> 
> Can it be because of data cache maintenance is required? Please see [1] for
> 
> more details, just a key note from there (Julien Grall):
> 
> "Per the hypercall ABI (see include/public/arch-arm.h) all the buffers must reside in memory which is mapped as Normal Inner Write-Back Inner-Shareable.
> You are passing non-cacheable memory, so the behavior you see is expected."

Please note that, as far as this patch is concerned, no hypervisor call
is used. What is done here is that all the accesses to memory mapped
sbsa-uart registers are trapped and emulated by the hypervisor (in my case,
Xen's mmio handler).

> Thank you,

BTW, what do you think of this patch?

-Takahiro Akashi

> Oleksandr
> 
> > * there is a prerequisite patch for Xen[2]
> >
> > The patch with xenguest_arm64_defconfig was tested on upstream Xen and
> > qemu-arm64.
> > (To work with xenguest_arm64_defconfig, minor and non-essential tweaks
> > are needed.)
> >
> > The output looks like:
> > U-Boot 2021.01-rc1-00005-g3b8e3cde5345 (Nov 04 2020 - 13:54:44 +0900) xenguest
> >
> > Xen virtual CPU
> > Model: XENVM-4.15
> > DRAM:  128 MiB
> > PVBLOCK: Failed to read device/vbd directory: ENOENT
> >
> > In:    sbsa-pl011
> > Out:   sbsa-pl011
> > Err:   sbsa-pl011
> > xenguest# dm tree
> >   Class     Index  Probed  Driver                Name
> > -----------------------------------------------------------
> >   root          0  [ + ]   root_driver           root_driver
> >   firmware      0  [   ]   psci                  |-- psci
> >   serial        0  [ + ]   serial_pl01x          |-- sbsa-pl011
> >   pvblock       0  [   ]   pvblock               `-- pvblock
> >
> > [1] https://urldefense.com/v3/__https://developer.arm.com/architectures/platform-design/server-systems__;!!GF_29dbcQIUBPA!k49FI4LUby7RffCuUHhIeq1ucvB2hhtch27HKXm3RBDLSY04ge4taCv7zqzDTat-6ZlDP1E68A$ [developer[.]arm[.]com]
> > [2] https://urldefense.com/v3/__https://lists.xenproject.org/archives/html/xen-devel/2020-10/msg02122.html__;!!GF_29dbcQIUBPA!k49FI4LUby7RffCuUHhIeq1ucvB2hhtch27HKXm3RBDLSY04ge4taCv7zqzDTat-6ZlHuV_0Rg$ [lists[.]xenproject[.]org]
> >
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> > ---
> >   drivers/serial/Kconfig                  | 13 +++++++++++--
> >   drivers/serial/serial_pl01x.c           | 16 +++++++++++++---
> >   include/dm/platform_data/serial_pl01x.h |  1 +
> >   3 files changed, 25 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
> > index b4805a2e4ea4..fb570174c577 100644
> > --- a/drivers/serial/Kconfig
> > +++ b/drivers/serial/Kconfig
> > @@ -332,6 +332,15 @@ config DEBUG_UART_PL011
> >   	  work. The driver will be available until the real driver model
> >   	  serial is running.
> >   
> > +config DEBUG_UART_SBSA
> > +	bool "sbsa-uart"
> > +	depends on PL01X_SERIAL
> > +	help
> > +	  Select this to enable a debug UART using the pl01x driver with the
> > +	  SBSA_UART type. You will need to provide parameters to make this
> > +	  work. The driver will be available until the real driver model
> > +	  serial is running.
> > +
> >   config DEBUG_UART_PIC32
> >   	bool "Microchip PIC32"
> >   	depends on PIC32_SERIAL
> > @@ -415,7 +424,7 @@ config DEBUG_UART_BASE
> >   
> >   config DEBUG_UART_CLOCK
> >   	int "UART input clock"
> > -	depends on DEBUG_UART
> > +	depends on DEBUG_UART && !DEBUG_UART_SBSA
> >   	default 0 if DEBUG_UART_SANDBOX
> >   	help
> >   	  The UART input clock determines the speed of the internal UART
> > @@ -427,7 +436,7 @@ config DEBUG_UART_CLOCK
> >   
> >   config DEBUG_UART_SHIFT
> >   	int "UART register shift"
> > -	depends on DEBUG_UART
> > +	depends on DEBUG_UART && !DEBUG_UART_SBSA
> >   	default 0 if DEBUG_UART
> >   	help
> >   	  Some UARTs (notably ns16550) support different register layouts
> > diff --git a/drivers/serial/serial_pl01x.c b/drivers/serial/serial_pl01x.c
> > index 2772c25f1d2d..5ef4ae0c6a65 100644
> > --- a/drivers/serial/serial_pl01x.c
> > +++ b/drivers/serial/serial_pl01x.c
> > @@ -84,6 +84,8 @@ static int pl01x_generic_serial_init(struct pl01x_regs *regs,
> >   		/* disable everything */
> >   		writel(0, &regs->pl011_cr);
> >   		break;
> > +	case TYPE_SBSA_UART:
> > +		break;
> >   	default:
> >   		return -EINVAL;
> >   	}
> > @@ -146,7 +148,8 @@ static int pl01x_generic_setbrg(struct pl01x_regs *regs, enum pl01x_type type,
> >   		writel(UART_PL010_CR_UARTEN, &regs->pl010_cr);
> >   		break;
> >   	}
> > -	case TYPE_PL011: {
> > +	case TYPE_PL011:
> > +	case TYPE_SBSA_UART: {
> >   		unsigned int temp;
> >   		unsigned int divider;
> >   		unsigned int remainder;
> > @@ -171,6 +174,9 @@ static int pl01x_generic_setbrg(struct pl01x_regs *regs, enum pl01x_type type,
> >   			writel(fraction, &regs->pl011_fbrd);
> >   		}
> >   
> > +		if (type == TYPE_SBSA_UART)
> > +			break;
> > +
> >   		pl011_set_line_control(regs);
> >   		/* Finally, enable the UART */
> >   		writel(UART_PL011_CR_UARTEN | UART_PL011_CR_TXE |
> > @@ -340,6 +346,7 @@ static const struct dm_serial_ops pl01x_serial_ops = {
> >   static const struct udevice_id pl01x_serial_id[] ={
> >   	{.compatible = "arm,pl011", .data = TYPE_PL011},
> >   	{.compatible = "arm,pl010", .data = TYPE_PL010},
> > +	{.compatible = "arm,sbsa-uart", .data = TYPE_SBSA_UART},
> >   	{}
> >   };
> >   
> > @@ -386,7 +393,8 @@ U_BOOT_DRIVER(serial_pl01x) = {
> >   
> >   #endif
> >   
> > -#if defined(CONFIG_DEBUG_UART_PL010) || defined(CONFIG_DEBUG_UART_PL011)
> > +#if defined(CONFIG_DEBUG_UART_PL010) || defined(CONFIG_DEBUG_UART_PL011) || \
> > +    defined(CONFIG_DEBUG_UART_SBSA)
> >   
> >   #include <debug_uart.h>
> >   
> > @@ -395,7 +403,9 @@ static void _debug_uart_init(void)
> >   #ifndef CONFIG_DEBUG_UART_SKIP_INIT
> >   	struct pl01x_regs *regs = (struct pl01x_regs *)CONFIG_DEBUG_UART_BASE;
> >   	enum pl01x_type type = CONFIG_IS_ENABLED(DEBUG_UART_PL011) ?
> > -				TYPE_PL011 : TYPE_PL010;
> > +				TYPE_PL011 :
> > +			       (CONFIG_IS_ENABLED(DEBUG_UART_PL010) ?
> > +				TYPE_PL010 : TYPE_SBSA_UART);
> >   
> >   	pl01x_generic_serial_init(regs, type);
> >   	pl01x_generic_setbrg(regs, type,
> > diff --git a/include/dm/platform_data/serial_pl01x.h b/include/dm/platform_data/serial_pl01x.h
> > index 77d96c49f03a..4bacbd512400 100644
> > --- a/include/dm/platform_data/serial_pl01x.h
> > +++ b/include/dm/platform_data/serial_pl01x.h
> > @@ -9,6 +9,7 @@
> >   enum pl01x_type {
> >   	TYPE_PL010,
> >   	TYPE_PL011,
> > +	TYPE_SBSA_UART,
> >   };
> >   
> >   /*
> [1] https://lists.xenproject.org/archives/html/xen-devel/2020-06/msg00737.html

More information about the U-Boot mailing list