From: Nick Kossifidis <mick@ics.forth.gr>
To: Gary Guo <gary@garyguo.net>
Cc: linux-riscv@lists.infradead.org
Subject: Re: [PATCH] riscv: enable TIME CSR in U mode
Date: Thu, 04 Mar 2021 19:35:00 +0200 [thread overview]
Message-ID: <e50f40a65f10e40c8d601791c0856cc6@mailhost.ics.forth.gr> (raw)
In-Reply-To: <20210216221208.2860-1-gary@garyguo.net>
Στις 2021-02-17 00:12, Gary Guo έγραψε:
> After ad5d112 we let the user mode to use rdtime directly for time
> access. This works if the hardware does not implement the TIME CSR
> and traps to the firmware. The spec however does allow a hardware
> implementation to redirect the CSR access to the memory-mapped MTIME
> CSR, and if this is performed it will check {M,S}COUNTEREN CSR to
> see if it is allowed.
>
> To prevent unhandled illegal instruction fault on these platforms,
> we can request these CSRs to be enabled in U-mode. For platforms
> that does not support the TIME CSR to MTIME CSR conversion, they
> will hardwire corresponding bit in COUNTEREN to zero and this would
> be a no-op.
>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> ---
> arch/riscv/kernel/head.S | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 0a4e81b8dc79..5a7a62190342 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -190,6 +190,9 @@ ENTRY(_start_kernel)
> .align 2
> pmp_done:
>
> + /* Allow user-mode to access time CSR */
> + csrw, CSR_MCOUNTEREN, 2
> +
> /*
> * The hartid in a0 is expected later on, and we have no firmware
> * to hand it to us.
> @@ -197,6 +200,9 @@ pmp_done:
> csrr a0, CSR_MHARTID
> #endif /* CONFIG_RISCV_M_MODE */
>
> + /* Allow user-mode to access time CSR */
> + csrw CSR_SCOUNTEREN, 2
> +
> /* Load the global pointer */
> .option push
> .option norelax
Shouldn't we use csrrs here to preserve current settings from the
firmware ? Also OpenSBI at this point sets both MCOUNTEREN/SCOUNTEREN to
-1, does anyone else modify that value ?
Regards,
Nick
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2021-03-04 17:35 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-16 22:12 [PATCH] riscv: enable TIME CSR in U mode Gary Guo
2021-03-04 17:35 ` Nick Kossifidis [this message]
2021-03-16 6:24 ` Gary Guo
2021-03-16 20:52 ` Nick Kossifidis
2021-03-17 2:50 ` Atish Patra
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=e50f40a65f10e40c8d601791c0856cc6@mailhost.ics.forth.gr \
--to=mick@ics.forth.gr \
--cc=gary@garyguo.net \
--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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.