From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F0C114654B for ; Thu, 28 Mar 2024 10:24:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711621497; cv=none; b=jJ043T9uiH2QpOtJRM4iAxicnP50Vui36QL5DfJdjyjaAjIYagPntVic/df7jt6SjBMDgS4KREsEW9gHU5aPxjPMkw2QpdSmy2cOR4IcLWKOfl5pyxqHSXkPvb4KrQtJBExYEF4q7Ha7QZ9gTxqWXqfs+v0uAsrEsENONtCY87Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711621497; c=relaxed/simple; bh=1cx1Xifn9yhAxfZ5u2l/0D09nOJTgLrcayVsJ8qGHPQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=H0g35GBHV4g0Q4BSmXcM6eLdlQrpQgx5bqtw1xDqOjKZ9q2TOHwzEKAxEjohW/+lMxRb1EBuBj8zrZUTDw4P8yRoPbQB0NR6QRezXS2HMaALgB1+jl1zH8gNjdgam7IO5LyXi63S/3xCybRZgDVQwabz/mpQ1BvFHfWq69/PkCY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bQK7GBDe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bQK7GBDe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09B64C433C7; Thu, 28 Mar 2024 10:24:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711621496; bh=1cx1Xifn9yhAxfZ5u2l/0D09nOJTgLrcayVsJ8qGHPQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bQK7GBDe1wsZlOAAMHiYgXEi6nC6ZSDIE6GsMksCXpsOEpueKiDPu5ma+SruGSoG4 KNMXCq9vhjZxFpBvLiUb5jo4C/VoUsNzUxxG/WyH2EueJBJCfhm4iStVss2jpxgxQm 1JKVnc+QMLCG9HnxTccidaDLw6C8XpFTf9hx8aKXCMyAPbI2kmybqdd5xsbZnzKmHf Vs+nQrtEbfk4sUxsTJ8IfmF0AGLdmxDhUEgVhK2NQ2NL004wgjOAbyf61BHvtyfd2p OLHoBf5AvQ29YSeymdVlGwpxcJKBIS1xdg/kkGsmatLvyja00DlrNZnIV0PupaMFIl 9PhTfVXgLKj7A== Date: Thu, 28 Mar 2024 18:11:32 +0800 From: Jisheng Zhang To: Samuel Holland Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Daniel Lezcano , Thomas Gleixner , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/5] riscv: nommu: use CSR_TIME* for get_cycles* implementation Message-ID: References: <20240325164021.3229-1-jszhang@kernel.org> <20240325164021.3229-3-jszhang@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Wed, Mar 27, 2024 at 12:29:13AM +0800, Jisheng Zhang wrote: > On Mon, Mar 25, 2024 at 09:39:26PM -0500, Samuel Holland wrote: > > Hi Jisheng, > > > > On 2024-03-25 11:40 AM, Jisheng Zhang wrote: > > > Per riscv privileged spec, "The time CSR is a read-only shadow of the > > > memory-mapped mtime register", "On RV32I the timeh CSR is a read-only > > > shadow of the upper 32 bits of the memory-mapped mtime register, while > > > time shadows only the lower 32 bits of mtime." Since get_cycles() only > > > reads the timer, it's fine to use CSR_TIME to implement get_cycles(). > > > > Unfortunately there are various implementations (e.g. FU740/Unmatched, probably > > K210 which this code was originally used for) which do not implement the time > > CSR, relying on M-mode software to emulate the CSR so S-mode software doesn't > > notice. So this code is needed to support those platforms when running Linux in > > M-mode. > > OOPS, I knew this for the first time there are such implementations > which doesn't implement the TIME CSR :( > > > > > Maybe there should be an option to assume the time CSR is/is not implemented, > > like there is for misaligned access? > > Yep, this seems the only solution. Then which should be the default > choice? I.E > > Assume all NOMMU goes through TIME CSR, and provide an option for > platform lacking of TIME CSR. This prefers TIME CSR. Hi all, v2 will prefer TIME CSR. Thanks > > VS. > > By default, MTIME is used, and provide one Kconfig option for TIME CSR > usage. This prefers MTIME > > which choice is better? Any suggestion? > > Thanks in advance > > > > > Regards, > > Samuel > > > > > Signed-off-by: Jisheng Zhang > > > --- > > > arch/riscv/include/asm/timex.h | 40 ---------------------------------- > > > 1 file changed, 40 deletions(-) > > > > > > diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h > > > index a06697846e69..a3fb85d505d4 100644 > > > --- a/arch/riscv/include/asm/timex.h > > > +++ b/arch/riscv/include/asm/timex.h > > > @@ -10,44 +10,6 @@ > > > > > > typedef unsigned long cycles_t; > > > > > > -#ifdef CONFIG_RISCV_M_MODE > > > - > > > -#include > > > - > > > -#ifdef CONFIG_64BIT > > > -static inline cycles_t get_cycles(void) > > > -{ > > > - return readq_relaxed(clint_time_val); > > > -} > > > -#else /* !CONFIG_64BIT */ > > > -static inline u32 get_cycles(void) > > > -{ > > > - return readl_relaxed(((u32 *)clint_time_val)); > > > -} > > > -#define get_cycles get_cycles > > > - > > > -static inline u32 get_cycles_hi(void) > > > -{ > > > - return readl_relaxed(((u32 *)clint_time_val) + 1); > > > -} > > > -#define get_cycles_hi get_cycles_hi > > > -#endif /* CONFIG_64BIT */ > > > - > > > -/* > > > - * Much like MIPS, we may not have a viable counter to use at an early point > > > - * in the boot process. Unfortunately we don't have a fallback, so instead > > > - * we just return 0. > > > - */ > > > -static inline unsigned long random_get_entropy(void) > > > -{ > > > - if (unlikely(clint_time_val == NULL)) > > > - return random_get_entropy_fallback(); > > > - return get_cycles(); > > > -} > > > -#define random_get_entropy() random_get_entropy() > > > - > > > -#else /* CONFIG_RISCV_M_MODE */ > > > - > > > static inline cycles_t get_cycles(void) > > > { > > > return csr_read(CSR_TIME); > > > @@ -60,8 +22,6 @@ static inline u32 get_cycles_hi(void) > > > } > > > #define get_cycles_hi get_cycles_hi > > > > > > -#endif /* !CONFIG_RISCV_M_MODE */ > > > - > > > #ifdef CONFIG_64BIT > > > static inline u64 get_cycles64(void) > > > { > >