linux-kernel - RE: [PATCH v3 1/2] cache: Add StarFive StarLink cache management for StarFive JH8100

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Date: Wed, 24 Apr 2024 15:26:52 +0000
From: Joshua Yeong <joshua.yeong@...rfivetech.com>
To: Emil Renner Berthing <emil.renner.berthing@...onical.com>,
	"robh@...nel.org" <robh@...nel.org>, "krzk+dt@...nel.org"
	<krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>,
	"conor@...nel.org" <conor@...nel.org>, "paul.walmsley@...ive.com"
	<paul.walmsley@...ive.com>, "palmer@...belt.com" <palmer@...belt.com>,
	"aou@...s.berkeley.edu" <aou@...s.berkeley.edu>, Leyfoon Tan
	<leyfoon.tan@...rfivetech.com>, JeeHeng Sia <jeeheng.sia@...rfivetech.com>
CC: "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>
Subject: RE: [PATCH v3 1/2] cache: Add StarFive StarLink cache management for
 StarFive JH8100

Emil Renner Berthing wrote: 
> Joshua Yeong wrote:
> > Emil Renner Berthing wrote:
> > > Joshua Yeong wrote:
> > > >
> > > >
> > > > Emil Renner Berthing wrote:
> > > > > Joshua Yeong wrote:
> > > > > > Emil Renner Berthing wrote:
> > > > > > > Joshua Yeong wrote:
> > > > > > > > Add StarFive Starlink cache management driver for
> > > > > > > > JH8100 SoC. This driver enables RISC-V non-standard cache
> > > > > > > > operation on
> > > > > > > > JH8100 that does not support Zicbom extension instructions.
> > > > > > > >
> > > > > > > > Signed-off-by: Joshua Yeong
> > > > > > > > <joshua.yeong@...rfivetech.com>
> > > > > > > > ---
> > > > > > > >  drivers/cache/Kconfig                   |   9 ++
> > > > > > > >  drivers/cache/Makefile                  |   5 +-
> > > > > > > >  drivers/cache/starfive_starlink_cache.c | 135
> > > > > > > > ++++++++++++++++++++++++
> > > > > > > >  3 files changed, 147 insertions(+), 2 deletions(-)
> > > > > > > > create mode
> > > > > > > > 100644 drivers/cache/starfive_starlink_cache.c
> > > > > > > >
> > > > > > > > diff --git a/drivers/cache/Kconfig b/drivers/cache/Kconfig
> > > > > > > > index
> > > > > > > > 9345ce4976d7..9181cd391f53 100644
> > > > > > > > --- a/drivers/cache/Kconfig
> > > > > > > > +++ b/drivers/cache/Kconfig
> > > > > > > > @@ -14,4 +14,13 @@ config SIFIVE_CCACHE
> > > > > > > >  	help
> > > > > > > >  	  Support for the composable cache controller on SiFive
> > > platforms.
> > > > > > > >
> > > > > > > > +config STARFIVE_STARLINK_CACHE
> > > > > > > > +	bool "StarFive StarLink Cache controller"
> > > > > > > > +	depends on RISCV
> > > > > > > > +	depends on ARCH_STARFIVE
> > > > > > > > +	select RISCV_DMA_NONCOHERENT
> > > > > > > > +	select RISCV_NONSTANDARD_CACHE_OPS
> > > > > > > > +	help
> > > > > > > > +	  Support for the StarLink cache controller on StarFive
> > > platforms.
> > > > > > >
> > > > > > > This is a bit misleading. The JH71x0s don't have this. It's
> > > > > > > only on the JH8100 so far, and hopefully later SoCs will
> > > > > > > just implement RISC-V
> > > > > standards for this.
> > > > > > > So maybe something like
> > > > > > >
> > > > > > > "Support for the StarLink cache controller on the StarFive JH8100
> SoC."
> > > > > > >
> > > > > >
> > > > > > Hi Emil,
> > > > > >
> > > > > > The StarLink-500 cache controller is not designed exclusively
> > > > > > for JH8100
> > > SoC.
> > > > > > While it is true that it currently exists on the StarFive
> > > > > > platform, CPU/SoC that does not come with Zicbom extensions
> > > > > > supported would need to rely on this cache drive to do cache
> > > > > > management operations. I think we don’t need to mentioned
> > > > > > 'JH8100
> > > SoC' here.
> > > > >
> > > > > Wait, in the previous mail you said that future designs will
> > > > > implement Zicbom and not need this work-around, but here you're
> > > > > talking about other SoCs that do need it. So which is it?
> > > >
> > > > If you visit the company website and look for StarLink-500, you
> > > > will find that it is a standalone IP that the company is selling
> > > > as an interconnect. Anyone who integrates StarLink without Zicbom
> > > > extensions may utilize the cache management operation from this IP.
> > >
> > > So then the "on StarFive platforms" part is wrong? Or will this
> > > always go together with the Dubhe cores?
> >
> > It would be 'on StarFive platform' without 'JH8100 SoC' that you suggested.
> > StarFive's newer cores that will have Zicbom extensions supported.
> > Those CPU core will not need to have this cache controller enabled.
> 
> No, what I meant was that if you're selling the "StarLink-500" IP to other SoC
> manufacturors then it will not be restricted to StarFive platforms. So then
> "Support for the StarLink cache controller _on StarFive platforms_" is no longer
> true, right?

Yes, you are right on this. AFAIK JH8100 integrates StarLink-500 and which is why 
we need this cache controller driver, I do not know who/what else products that 
might use this IP.

> 
> /Emil