linux-kernel - Re: [PATCH v2] hvc_dcc : add support to armv4 and armv5 core

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Message-ID: <5040EAF7.9010003@codeaurora.org>
Date:	Fri, 31 Aug 2012 09:48:55 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Matthieu CASTET <castet.matthieu@...e.fr>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	gregkh@...uxfoundation.org, arnd@...db.de,
	alan@...rguk.ukuu.org.uk,
	Matthieu Castet <matthieu.castet@...rot.com>
Subject: Re: [PATCH v2] hvc_dcc : add support to armv4 and armv5 core

On 8/31/2012 4:47 AM, Matthieu CASTET wrote:
> Signed-off-by: Matthieu Castet <matthieu.castet@...rot.com>

Please consider adding some sort of commit text. Does this add some new
feature I may want on some downstream distro kernel?

> @@ -51,7 +51,7 @@ static inline char __dcc_getchar(void)
>  	return __c;
>  }
>  
> -static inline void __dcc_putchar(char c)
> +static inline void __dcc_putchar_v6(char c)
>  {
>  	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
>  		: /* no output register */
> @@ -59,6 +59,69 @@ static inline void __dcc_putchar(char c)
>  	isb();
>  }
>  
> +static int hvc_dcc_put_chars_v6(uint32_t vt, const char *buf, int count)
> +{
> +	int i;
> +
> +	for (i = 0; i < count; i++) {
> +		while (__dcc_getstatus_v6() & DCC_STATUS_TX_V6)
> +			cpu_relax();
> +
> +		__dcc_putchar_v6(buf[i]);
> +	}
> +
> +	return count;
> +}

It's unfortunate that the main logic is duplicated. I wonder if we could
push the runtime decision slightly lower into the accessor functions
instead and make some new functions dcc_tx_busy() and dcc_rx_busy() or
something. Then these loops stay the same.

> +
> +static int hvc_dcc_get_chars_v6(uint32_t vt, char *buf, int count)
> +{
> +	int i;
> +
> +	for (i = 0; i < count; ++i)
> +		if (__dcc_getstatus_v6() & DCC_STATUS_RX_V6)
> +			buf[i] = __dcc_getchar_v6();
> +		else
> +			break;
> +
> +	return i;
> +}
> +
> +static const struct hv_ops hvc_dcc_get_put_ops_v6 = {
> +	.get_chars = hvc_dcc_get_chars_v6,
> +	.put_chars = hvc_dcc_put_chars_v6,
> +};
> +
> +#define DCC_STATUS_RX		(1 << 0)
> +#define DCC_STATUS_TX		(1 << 1)
> +
> +/* primitive JTAG1 protocol utilities */

This comment doesn't tell me much. Remove it?

> +static inline u32 __dcc_getstatus(void)
> +{
> +	u32 ret;
> +
> +	asm __volatile__ ("mrc p14, 0, %0, c0, c0	@ read comms ctrl reg"
> +		: "=r" (ret));

Can you use volatile instead of __volatile__ so that the file is consistent?

> +
> +	return ret;
> +}
> +
> +static inline char __dcc_getchar(void)
> +{
> +	char c;
> +
> +	asm __volatile__ ("mrc p14, 0, %0, c1, c0	@ read comms data reg"
> +		: "=r" (c));
> +

Do you see any multiple character inputs? I think you may need an isb
here similar to the v6/7 code and in the putchar as well.

> +	return c;
> +}
> +
> +static inline void __dcc_putchar(unsigned char c)
> +{
> +	asm __volatile__ ("mcr p14, 0, %0, c1, c0	@ write a char"
> +		: /* no output register */
> +		: "r" (c));
> +}
> +
>  static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
>  {
>  	int i;
>

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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