Re: openbmc Digest, Vol 32, Issue 32

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2018-04-12 at 16:42 +0800, Wang, Haiyue wrote:
> 
> I means the device tree merge time, putting things in kernel need long time
> to be passed code review. And people may want to export different range of
> registers, then they need to change the device tree, the development cycle
> may be long.

But that's not a big issue in practice though, you don't *need* all
your device-trees to be upstream and up to date especially if it's
stored separately from the kernel.

Keep in mind this should be strictly limited to a few registers that
need that sort of manipulation, maybe a handful or two, that's it.

Most things need proper kernel drivers.

> > > to finish the soc setting. But Facebook just uses user app, this
> > > development is fast, and
> > > 
> > > simple is the best.
> > 
> > Sorry I don't really get what you mean. Please elaborate.
> > 
> > > Well, just for sharing what I found, I may misunderstood the BIG idea
> > > after this kernel
> > 
> > The basic idea is to have a mechanism by which the SoC code in the
> > kernel can expose to userspace via sysfs a *small* selected set of
> > tunables that userspace might have to tweak for various platform
> > specific reasons.
> > 
> > To qualify, these things have to strictly be things that don't fit
> > within any existing Linux ABI and subsystem, and typically that affect
> > the *host* and not the BMC itself (or to a very limited extent).
> > 
> > Some examples are the tunables to control whether the host can access
> > the AHB bus via the backdoor on LPC or PCIe (and if yes which regions
> > are enabled).
> 
> I see, I just think Facebook's method is more common and flexible, but 
> of course,
> it has the security reason you mentioned. :)
> > > patch design. :-)
> > > 
> > > 
> > > soc_gpio_table = {
> > > 
> > > 	'A10': [
> > > 
> > > 	Function('SDA3', BitsEqual(0x90, [16], 0x1)),
> > > 
> > > 	Function('GPIOQ1', None)
> > > 
> > > 	],
> > > 
> > > 	'A11': [
> > > 
> > > 	Function('SCL3', BitsEqual(0x90, [16], 0x1)),
> > > 
> > > 	Function('GPIOQ0', None)
> > > 
> > > 	],
> > > 
> > > https://github.com/facebook/openbmc/blob/helium/common/recipes-utils/openbmc-gpio/files/openbmc-gpio-1/phymemory.py
> > > 
> > > https://github.com/facebook/openbmc/blob/helium/meta-aspeed/recipes-utils/ast-mdio/files/ast-mdio.py
> > > 
> > > https://github.com/facebook/openbmc/blob/helium/meta-aspeed/recipes-utils/openbmc-gpio/files/openbmc-gpio-1/ast2500_gpio_table.py
> > 
> > I don't undertsand what those links are supposed to be. Please
> > elaborate on what you mean rather than posting random links.
> 
> Just want to say the code layer is flexible for different products and 
> different
> BMC chip vendors. Sorry to confuse you so much, thanks for your reply. :)
> > Cheers,
> > Ben.
> > 
> > 
> > > BR,
> > > 
> > > Haiyue
> > > 
> > > 
> > > On 2018-04-12 13:32, openbmc-request@lists.ozlabs.org wrote:
> > > > Message: 1
> > > > Date: Thu, 12 Apr 2018 13:21:43 +0930
> > > > From: Andrew Jeffery<andrew@aj.id.au>
> > > > To:openbmc@lists.ozlabs.org
> > > > Cc: Andrew Jeffery<andrew@aj.id.au>,joel@jms.id.au,jk@ozlabs.org,
> > > > 	benh@kernel.crashing.org
> > > > Subject: [RFC PATCH linux dev-4.13 1/3] soc: aspeed: Miscellaneous
> > > > 	control interfaces
> > > > Message-ID:<20180412035145.21488-2-andrew@aj.id.au>
> > > > 
> > > > The ASPEED BMC SoCs have many knobs and switches that are sometimes
> > > > design-specific and often defy any approach to unify them under an
> > > > existing subsystem.
> > > > 
> > > > Add a driver to translate a devicetree table into sysfs entries to
> > > > expose bits and fields for manipulation from userspace. This encompasses
> > > > concepts from scratch registers to boolean conditions to enable or
> > > > disable host interface features.
> > > > 
> > > > Signed-off-by: Andrew Jeffery<andrew@aj.id.au>
> > > > ---
> > > >    drivers/soc/Kconfig                  |   1 +
> > > >    drivers/soc/Makefile                 |   1 +
> > > >    drivers/soc/aspeed/Kconfig           |  11 +++
> > > >    drivers/soc/aspeed/Makefile          |   1 +
> > > >    drivers/soc/aspeed/aspeed-bmc-misc.c | 187 +++++++++++++++++++++++++++++++++++
> > > >    5 files changed, 201 insertions(+)
> > > >    create mode 100644 drivers/soc/aspeed/Kconfig
> > > >    create mode 100644 drivers/soc/aspeed/Makefile
> > > >    create mode 100644 drivers/soc/aspeed/aspeed-bmc-misc.c
> > > > 
> > > > diff --git a/drivers/soc/Kconfig b/drivers/soc/Kconfig
> > > > index 07fc0ac51c52..776fd5978f70 100644
> > > > --- a/drivers/soc/Kconfig
> > > > +++ b/drivers/soc/Kconfig
> > > > @@ -1,6 +1,7 @@
> > > >    menu "SOC (System On Chip) specific Drivers"
> > > >    
> > > >    source "drivers/soc/actions/Kconfig"
> > > > +source "drivers/soc/aspeed/Kconfig"
> > > >    source "drivers/soc/atmel/Kconfig"
> > > >    source "drivers/soc/bcm/Kconfig"
> > > >    source "drivers/soc/fsl/Kconfig"
> > > > diff --git a/drivers/soc/Makefile b/drivers/soc/Makefile
> > > > index 9241125416ba..94a5b97c4466 100644
> > > > --- a/drivers/soc/Makefile
> > > > +++ b/drivers/soc/Makefile
> > > > @@ -3,6 +3,7 @@
> > > >    #
> > > >    
> > > >    obj-$(CONFIG_ARCH_ACTIONS)	+= actions/
> > > > +obj-$(CONFIG_ARCH_ASPEED)       += aspeed/
> > > >    obj-$(CONFIG_ARCH_AT91)		+= atmel/
> > > >    obj-y				+= bcm/
> > > >    obj-$(CONFIG_ARCH_DOVE)		+= dove/
> > > > diff --git a/drivers/soc/aspeed/Kconfig b/drivers/soc/aspeed/Kconfig
> > > > new file mode 100644
> > > > index 000000000000..704a4efe180f
> > > > --- /dev/null
> > > > +++ b/drivers/soc/aspeed/Kconfig
> > > > @@ -0,0 +1,11 @@
> > > > +menu "ASPEED SoC drivers"
> > > > +
> > > > +config ASPEED_BMC_MISC
> > > > +	bool "Miscellaneous ASPEED BMC interfaces"
> > > > +	depends on ARCH_ASPEED || COMPILE_TEST
> > > > +	default ARCH_ASPEED
> > > > +	help
> > > > +	  Say yes to expose VGA and LPC scratch registers, and other
> > > > +	  miscellaneous control interfaces specific to the ASPEED BMC SoCs
> > > > +
> > > > +endmenu