RE: [PATCH] ARM: Add support for Realtek SOC

From: James Tai <james.tai@realtek.com>
To: "'Arnd Bergmann'" <arnd@arndb.de>
Cc: "jamestai.sky@gmail.com" <jamestai.sky@gmail.com>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Russell King" <linux@armlinux.org.uk>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Paul Burton" <paul.burton@mips.com>,
	"Masahiro Yamada" <yamada.masahiro@socionext.com>,
	"Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
	"Mike Rapoport" <rppt@linux.ibm.com>,
	"Doug Anderson" <armlinux@m.disordat.com>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"Benjamin Gaignard" <benjamin.gaignard@linaro.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Stefan Agner" <stefan@agner.ch>,
	"Nicolas Pitre" <nico@fluxnic.net>,
	"Thierry Reding" <treding@nvidia.com>,
	"Jason A . Donenfeld" <Jason@zx2c4.com>,
	"Rob Herring" <robh@kernel.org>,
	"CY_Huang[黃鉦晏]" <cy.huang@realtek.com>,
	"Phinex Hung" <phinex@realtek.com>,
	"Andreas Färber" <afaerber@suse.de>,
	"Lorenzo Pieralisi" <Lorenzo.Pieralisi@arm.com>
Subject: RE: [PATCH] ARM: Add support for Realtek SOC
Date: Mon, 23 Sep 2019 02:25:43 +0000	[thread overview]
Message-ID: <43B123F21A8CFE44A9641C099E4196FFCF8E7CA5@RTITMBSVM04.realtek.com.tw> (raw)
In-Reply-To: <CAK8P3a39VrC1Xn+HZc5gvh1-nUYKywDGjTfO9WPCqim89WtGAg@mail.gmail.com>

> <james.tai@realtek.com> wrote:
> > > Subject: Re: [PATCH] ARM: Add support for Realtek SOC
> 
> > > > @@ -148,6 +148,7 @@ endif
> > > >  textofs-$(CONFIG_ARCH_MSM8X60) := 0x00208000
> > > >  textofs-$(CONFIG_ARCH_MSM8960) := 0x00208000
> > > >  textofs-$(CONFIG_ARCH_MESON) := 0x00208000
> > > > +textofs-$(CONFIG_ARCH_REALTEK) := 0x00208000
> > > >  textofs-$(CONFIG_ARCH_AXXIA) := 0x00308000
> > >
> > > Can you explain why this is needed for your platform?
> > >
> > We need to reserve memory (0x00000000 ~ 0x001B0000) for rom and boot
> code.
> 
> Ok.
> 
> > > > +config ARCH_RTD16XX
> > > > +       bool "Enable support for RTD1619"
> > > > +       depends on ARCH_REALTEK
> > > > +       select ARM_GIC_V3
> > > > +       select ARM_PSCI
> > >
> > > As I understand, this chip uses a Cortex-A55. What is the reason for
> > > adding support only to the 32-bit ARM architecture rather than 64-bit?
> >
> > The RTD16XX platform also support the 64-bit ARM architecture.
> > I will add the 64-bit ARM architecture in new version patch.
> >
> > > Most 64-bit SoCs are only supported with arch/arm64, but generally
> > > speaking that is not a requirement. My rule of thumb is that on
> > > systems with 1GB of RAM or more, one would want to run a 64-bit
> > > kernel, while systems with less than that are better off with a
> > > 32-bit one, but that is clearly not the only reason for picking one over the
> other.
> > >
> > Support 32-bit ARM architecture is for application compatibility.
> 
> Generally speaking, a 64-bit kernel should work better on 64-bit hardware
> even when you are running mostly 32-bit applications. However, you may have
> device drivers that do not correctly set compat_ioctl handlers.
> 
> As I said, it's no problem to allow both, just explain this in the changelog text
> for the driver, along with the need for the textofs setting.
> 
OK.

> > > It's very unusual to see custom smp operations on an ARMv8 system,
> > > as we normally use PSCI here. Can you explain what is going on here?
> > > Are you able to use a boot wrapper that implements these in psci instead?
> > >
> > The smp operations is porting form other Realtek platform.
> >
> > Currently, The RTD16XX platform can use the PSCI method.
> > I will add PSCI method in new version patch.
> 
> Ok, perfect!
> 
> > > > +       timer_probe();
> > > > +       tick_setup_hrtimer_broadcast(); }
> > >
> > > What do you need tick_setup_hrtimer_broadcast() for? I don't see any
> > > other platform calling this.
> > >
> > I want to initialize the HR timer.
> 
> I'm still unsure about this one. My feeling is that it should not be in the
> platform code, but I don't quite understand which hardware needs it. I see that
> Lorenzo Pieralisi added the same code to arm64 in commit 9358d755bd5c
> ("arm64: kernel: initialize broadcast hrtimer based clock event device"), but
> nothing ever calls it on 32-bit arch/arm even though the code does get built in
> to the kernel.

I will add the 'hrtimer' initialization flow in related devices drivers.

> My feeling is that either you don't really need it, or this is something that other
> platforms should really do as well, and it should be called from the generic
> time_init() function in arch/arm/kernel/time.c instead.
> 
OK. I understand.

> Can you try to find out more of the background here, and then move the call to
> time_init() assuming it is indeed useful?

I agree with you. It is not necessary to call 'time_init()' function in platform code.

>        Arnd
> 
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