From: alankao@andestech.com (Alan Kao)
To: linux-riscv@lists.infradead.org
Subject: [RFC 0/2] RISC-V: A proposal to add vendor-specific code
Date: Fri, 2 Nov 2018 08:41:22 +0800 [thread overview]
Message-ID: <20181102004122.GA22741@andestech.com> (raw)
In-Reply-To: <mhng-22ded2c8-7f87-4acc-b017-627e369cf874@palmer-si-x1c4>
On Thu, Nov 01, 2018 at 10:50:04AM -0700, Palmer Dabbelt wrote:
> On Wed, 31 Oct 2018 17:55:42 PDT (-0700), alankao at andestech.com wrote:
> >On Wed, Oct 31, 2018 at 07:17:45AM -0700, Christoph Hellwig wrote:
> >>On Wed, Oct 31, 2018 at 04:46:10PM +0530, Anup Patel wrote:
> >>> I agree that we need a place for vendor-specific ISA extensions and
> >>> having vendor-specific directories is also good.
> >>
> >>The only sensible answer is that we should not allow vendor specific
> >>extensions in the kernel at all. ...
> >
> >How can this even be possible if a extension includes an extra register
> >set as some domain-specific context? In such a case, kernel should
> >at least process the context during any context switch, just like how it
> >deals with the FP context.
>
> Ya, I think there are cases where vendor-specific extensions are going to be
> necessary to handle within the kernel. Right now the only one I can think
> of is the performance counter stuff, where we explicitly allow
> vendor-specific counters as part of the ISA spec.
>
> For stateful extensions, we currently have a standard mechanism where the XS
> bits get set in sstatus and the actual save/restore code is hidden behind an
> SBI call. That call doesn't currently exist, but if we just go ahead and
> add one it should be easy to support this from within Linux. We'll need to
> figure out how to enable these custom extensions from userspace, but that
> seems tractable as well. We'll probably also want some fast-path for the V
> extension (and any other stateful standard extensions), but I think as long
> as the V extension adds a quick check for dirtiness then it's not a big
> deal.
>
> Do you guys have stateful extensions? We're trying really hard to avoid
> them at SiFive because they're a huge headache, so unless there's a
> compelling base of software using one I don't want to go add support if we
> can avoid it.
Currently no, but the future is hard to see. As long as the extensible freedom
claimed by the RISC-V foundation remains true, such extensions may have their
role to play. Don't worry now, I was just to give a example that in some
possible vendor-specific cases the kernel cannot keep itself from involving.
WARNING: multiple messages have this Message-ID (diff)
From: Alan Kao <alankao@andestech.com>
To: Palmer Dabbelt <palmer@sifive.com>
Cc: zong@andestech.com, aou@eecs.berkeley.edu,
Arnd Bergmann <arnd@arndb.de>,
greentime@andestech.com, anup@brainfault.org,
linux-kernel@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
vincentc@andestech.com, linux-riscv@lists.infradead.org,
deanbo422@gmail.com
Subject: Re: [RFC 0/2] RISC-V: A proposal to add vendor-specific code
Date: Fri, 2 Nov 2018 08:41:22 +0800 [thread overview]
Message-ID: <20181102004122.GA22741@andestech.com> (raw)
Message-ID: <20181102004122.vGOBQZwqy2VhSw1CyuKRuIsvsH-F90CnsOT9r17fk9Y@z> (raw)
In-Reply-To: <mhng-22ded2c8-7f87-4acc-b017-627e369cf874@palmer-si-x1c4>
On Thu, Nov 01, 2018 at 10:50:04AM -0700, Palmer Dabbelt wrote:
> On Wed, 31 Oct 2018 17:55:42 PDT (-0700), alankao@andestech.com wrote:
> >On Wed, Oct 31, 2018 at 07:17:45AM -0700, Christoph Hellwig wrote:
> >>On Wed, Oct 31, 2018 at 04:46:10PM +0530, Anup Patel wrote:
> >>> I agree that we need a place for vendor-specific ISA extensions and
> >>> having vendor-specific directories is also good.
> >>
> >>The only sensible answer is that we should not allow vendor specific
> >>extensions in the kernel at all. ...
> >
> >How can this even be possible if a extension includes an extra register
> >set as some domain-specific context? In such a case, kernel should
> >at least process the context during any context switch, just like how it
> >deals with the FP context.
>
> Ya, I think there are cases where vendor-specific extensions are going to be
> necessary to handle within the kernel. Right now the only one I can think
> of is the performance counter stuff, where we explicitly allow
> vendor-specific counters as part of the ISA spec.
>
> For stateful extensions, we currently have a standard mechanism where the XS
> bits get set in sstatus and the actual save/restore code is hidden behind an
> SBI call. That call doesn't currently exist, but if we just go ahead and
> add one it should be easy to support this from within Linux. We'll need to
> figure out how to enable these custom extensions from userspace, but that
> seems tractable as well. We'll probably also want some fast-path for the V
> extension (and any other stateful standard extensions), but I think as long
> as the V extension adds a quick check for dirtiness then it's not a big
> deal.
>
> Do you guys have stateful extensions? We're trying really hard to avoid
> them at SiFive because they're a huge headache, so unless there's a
> compelling base of software using one I don't want to go add support if we
> can avoid it.
Currently no, but the future is hard to see. As long as the extensible freedom
claimed by the RISC-V foundation remains true, such extensions may have their
role to play. Don't worry now, I was just to give a example that in some
possible vendor-specific cases the kernel cannot keep itself from involving.
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2018-11-02 0:41 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-31 10:35 [RFC 0/2] RISC-V: A proposal to add vendor-specific code Vincent Chen
2018-10-31 10:35 ` Vincent Chen
2018-10-31 10:35 ` [RFC 1/2] RISC-V: An infrastructure " Vincent Chen
2018-10-31 10:35 ` Vincent Chen
2018-10-31 10:35 ` [RFC 2/2] RISC-V: make dma_map_ops work without cache coherent agent Vincent Chen
2018-10-31 10:35 ` Vincent Chen
2018-10-31 11:16 ` [RFC 0/2] RISC-V: A proposal to add vendor-specific code Anup Patel
2018-10-31 11:16 ` Anup Patel
2018-10-31 11:45 ` Arnd Bergmann
2018-10-31 11:45 ` Arnd Bergmann
2018-10-31 14:17 ` Christoph Hellwig
2018-10-31 14:17 ` Christoph Hellwig
2018-11-01 0:55 ` Alan Kao
2018-11-01 0:55 ` Alan Kao
2018-11-01 17:50 ` Palmer Dabbelt
2018-11-01 17:50 ` Palmer Dabbelt
2018-11-02 0:41 ` Alan Kao [this message]
2018-11-02 0:41 ` Alan Kao
2018-10-31 17:27 ` Palmer Dabbelt
2018-10-31 17:27 ` Palmer Dabbelt
2018-10-31 19:17 ` Olof Johansson
2018-10-31 19:17 ` Olof Johansson
2018-11-01 17:48 ` Karsten Merker
2018-11-05 6:58 ` Vincent Chen
2018-11-05 6:58 ` Vincent Chen
2018-11-05 7:05 ` Christoph Hellwig
2018-11-05 7:05 ` Christoph Hellwig
2018-11-05 8:52 ` Arnd Bergmann
2018-11-05 8:52 ` Arnd Bergmann
2018-11-05 9:08 ` Christoph Hellwig
2018-11-05 9:08 ` Christoph Hellwig
2018-11-05 13:51 ` Arnd Bergmann
2018-11-05 13:51 ` Arnd Bergmann
2018-11-06 6:59 ` Christoph Hellwig
2018-11-06 6:59 ` Christoph Hellwig
2018-11-06 23:45 ` Palmer Dabbelt
2018-11-06 23:45 ` Palmer Dabbelt
2018-11-07 9:51 ` Arnd Bergmann
2018-11-07 9:51 ` Arnd Bergmann
2018-11-06 23:45 ` Palmer Dabbelt
2018-11-06 23:45 ` Palmer Dabbelt
2018-11-08 2:43 ` Vincent Chen
2018-11-08 2:43 ` Vincent Chen
2018-11-05 19:39 ` Nick Kossifidis
2018-11-05 19:39 ` Nick Kossifidis
2018-11-06 6:56 ` Christoph Hellwig
2018-11-06 6:56 ` Christoph Hellwig
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181102004122.GA22741@andestech.com \
--to=alankao@andestech.com \
--cc=linux-riscv@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).