linux-kernel - Re: [PATCH 4/4] msm: scm: Get cacheline size from CTR

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Date:	Thu, 24 Feb 2011 20:01:26 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Stephen Boyd <sboyd@...eaurora.org>
cc:	David Brown <davidb@...eaurora.org>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 4/4] msm: scm: Get cacheline size from CTR

On Thu, 24 Feb 2011, Stephen Boyd wrote:

> Instead of hardcoding the cacheline size as 32, get the cacheline
> size from the CTR register.
> 
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> ---
>  arch/arm/mach-msm/scm.c |   17 ++++++++++++-----
>  1 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/mach-msm/scm.c b/arch/arm/mach-msm/scm.c
> index cfa808d..0528c71 100644
> --- a/arch/arm/mach-msm/scm.c
> +++ b/arch/arm/mach-msm/scm.c
> @@ -26,9 +26,6 @@
>  
>  #include "scm.h"
>  
> -/* Cache line size for msm8x60 */
> -#define CACHELINESIZE 32
> -
>  #define SCM_ENOMEM		-5
>  #define SCM_EOPNOTSUPP		-4
>  #define SCM_EINVAL_ADDR		-3
> @@ -207,6 +204,14 @@ static int __scm_call(const struct scm_command *cmd)
>  	return ret;
>  }
>  
> +static inline u32 dcache_line_size(void)
> +{
> +	u32 ctr;
> +
> +	asm volatile("mrc p15, 0, %0, c0, c0, 1" : "=r" (ctr));
> +	return 4 << ((ctr >> 16) & 0xf);
> +}
> +
>  /**
>   * scm_call() - Send an SCM command
>   * @svc_id: service identifier
> @@ -243,11 +248,13 @@ int scm_call(u32 svc_id, u32 cmd_id, const void *cmd_buf, size_t cmd_len,
>  	do {
>  		u32 start = (u32)rsp;
>  		u32 end = (u32)scm_get_response_buffer(rsp) + resp_len;
> -		start &= ~(CACHELINESIZE - 1);
> +		u32 cacheline_size = dcache_line_size();

And why do you want to do that on every scm_call() invocation and on
every loop of that code? If your dcache_line_size() changes at
runtime, then you might have other problems.

Thanks,

	tglx


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