Re: [PATCH v1 1/2] riscv: Kconfig: Allow RV32 to build with no MMU

Conor Dooley
2023-01-20T20:48:24Z

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On Fri, Jan 20, 2023 at 08:44:10PM +0000, Conor Dooley wrote:
> On Fri, Jan 20, 2023 at 12:39:06PM -0500, Jesse Taube wrote:
> > On 1/20/23 02:59, Conor Dooley wrote:
> > > Since you'll have to re-submit, making sure that allowing !MMU on rv32
> > > doesn't break the build due to canaan k210 drivers being enabled despite
> > > relying on 64-bit divisions, I've got some nits for you.
> > Not sure what driver needs 64bit, but sense !MMU was only selected by 64BIT.
>
> LKP reported a build error for it:
> https://lore.kernel.org/linux-riscv/202301201538.zNlqgE4L-lkp@intel.com/
>
> > This should work.
> > diff --git a/arch/riscv/Kconfig.socs b/arch/riscv/Kconfig.socs
> > index 69774bb362d6..b9835b8ede86 100644
> > --- a/arch/riscv/Kconfig.socs
> > +++ b/arch/riscv/Kconfig.socs
> > @@ -43,7 +43,7 @@ config SOC_VIRT
> >
> > config SOC_CANAAN
> > bool "Canaan Kendryte K210 SoC"
> > - depends on !MMU
> > + depends on !MMU && 64BIT
> > select CLINT_TIMER if RISCV_M_MODE
> > select SERIAL_SIFIVE if TTY
> > select SERIAL_SIFIVE_CONSOLE if TTY
>
> I don't think this is the correct fix for the problem - the drivers
> really should not do implicit 64-bit divisions IMO.
> Linux has division helpers for them in math64.h.
> None of the other SoCs have a dependency on 64BIT and I'd not been keen
> on adding on here.
>
> I suspect the fix is as simple as the below, but I'd need to go test it.
>
> Thanks,
> Conor.
>
> --- 8< ---
> From ecfa79ad1b24f68cfccb77d666e443293d52d066 Mon Sep 17 00:00:00 2001
> From: Conor Dooley <conor.dooley@microchip.com>
> Date: Fri, 20 Jan 2023 20:36:29 +0000
> Subject: [PATCH] clk: k210: remove an implicit 64-bit division
>
> The K210 clock driver depends on SOC_CANAAN, which is only selectable
> when !MMU on RISC-V. !MMU is not possible on 32-bit yet, but patches
> have been sent for its enabling. The kernel test robot reported this
> implicit 64-bit division there.
>
> Replace the implicit division with an explicit one.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/linux-riscv/202301201538.zNlqgE4L-lkp@intel.com/
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
> Since it was always guarded such that it only ever built for 64-bit, I
> am not sure that a fixes tag is needed, but it would be:
> Fixes: c6ca7616f7d5 ("clk: Add RISC-V Canaan Kendryte K210 clock driver")
> ---
> drivers/clk/clk-k210.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/clk/clk-k210.c b/drivers/clk/clk-k210.c
> index 67a7cb3503c3..17c5bfb384ad 100644
> --- a/drivers/clk/clk-k210.c
> +++ b/drivers/clk/clk-k210.c
> @@ -495,7 +495,7 @@ static unsigned long k210_pll_get_rate(struct clk_hw *hw,
> f = FIELD_GET(K210_PLL_CLKF, reg) + 1;
> od = FIELD_GET(K210_PLL_CLKOD, reg) + 1;
>
> - return (u64)parent_rate * f / (r * od);
> + return div_u64(parent_rate * f, r * od);

Nope, that's wrong. I omitted the cast...

return div_u64((u64)parent_rate * f, r * od);

> }
>
> static const struct clk_ops k210_pll_ops = {
> --
> 2.39.0
>

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