[PATCH v2] riscv: cancel the limitation that NR_CPUS is less than or equal to 32

[Xiang W]

在 2023-02-10星期五的 07:25 +0000，Leo Liang写道：
> Hi Xiang,
> 
> On Fri, Feb 03, 2023 at 03:24:37PM +0100, David Abdurachmanov wrote:
> > On Mon, Jan 3, 2022 at 1:13 PM Leo Liang <ycliang at andestech.com> wrote:
> > > 
> > > On Thu, Dec 30, 2021 at 01:55:15AM +0800, Xiang W wrote:
> > > > 在 2021-12-29星期三的 17:23 +0800，Leo Liang写道：
> > > > > Hi Xiang,
> > > > > On Wed, Dec 22, 2021 at 07:32:53AM +0800, Xiang W wrote:
> > > > > > Various specifications of riscv allow the number of hart to be
> > > > > > greater than 32. The limit of 32 is determined by
> > > > > > gd->arch.available_harts. We can eliminate this limitation through
> > > > > > bitmaps. Currently, the number of hart is limited to 4095, and 4095
> > > > > > is the limit of the RISC-V Advanced Core Local Interruptor
> > > > > > Specification.
> > > > > > 
> > > > > > Test on sifive unmatched.
> > > > > > 
> > > > > > Signed-off-by: Xiang W <wxjstz at 126.com>
> > > > > > ---
> > > > > > Changes since v1:
> > > > > > 
> > > > > > * When NR_CPUS is very large, the value of GD_AVAILABLE_HARTS will
> > > > > >   overflow the immediate range of ld/lw. This patch fixes this
> > > > > >   problem
> > > > > > 
> > > > > >  arch/riscv/Kconfig                   |  4 ++--
> > > > > >  arch/riscv/cpu/start.S               | 21 ++++++++++++++++-----
> > > > > >  arch/riscv/include/asm/global_data.h |  4 +++-
> > > > > >  arch/riscv/lib/smp.c                 |  2 +-
> > > > > >  4 files changed, 22 insertions(+), 9 deletions(-)
> > > > > > 
> > 
> > I noticed that this has never landed in U-Boot. Was this forgotten or
> > dropped for some reason (couldn't find anything)?
> > 
> > The current limit on the Linux kernel side is 512. The default on
> > 64-bit (riscv64) is 64.
> > 
> > david
> 
> The patch seems to cause some CI error (timeout on QEMU).
> (https://source.denx.de/u-boot/custodians/u-boot-riscv/-/pipelines/15076)
> Could you take a look at it if you have time?
> 
> Best regards,
> Leo

sorry! I missing a bug. There is an error in calculating the starting address
of available_harts. The patch for start.S needs to be updated.

diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index 76850ec9be..92f3b78f29 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -166,11 +166,22 @@ wait_for_gd_init:
 	mv	gp, s0
 
 	/* register available harts in the available_harts mask */
-	li	t1, 1
-	sll	t1, t1, tp
-	LREG	t2, GD_AVAILABLE_HARTS(gp)
-	or	t2, t2, t1
-	SREG	t2, GD_AVAILABLE_HARTS(gp)
+	li	t1, GD_AVAILABLE_HARTS
+	add	t1, t1, gp
+#if defined(CONFIG_ARCH_RV64I)
+	srli	t2, tp, 6
+	slli	t2, t2, 3
+#elif defined(CONFIG_ARCH_RV32I)
+	srli	t2, tp, 5
+	slli	t2, t2, 2
+#endif
+	add	t1, t1, t2
+	LREG	t2, 0(t1)
+	li	t3, 1
+	sll	t3, t3, tp
+	or	t2, t2, t3
+	SREG	t2, 0(t1)
 
 	amoswap.w.rl zero, zero, 0(t0)

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