linux-kernel - Re: [PATCH 1/3] ARM: OMAP2+: gpmc: Fix writing in gpmc_cs_set

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Date:	Mon, 26 Jan 2015 11:34:50 +0200
From:	Roger Quadros <rogerq@...com>
To:	Semen Protsenko <semen.protsenko@...ballogic.com>,
	Tony Lindgren <tony@...mide.com>
CC:	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] ARM: OMAP2+: gpmc: Fix writing in gpmc_cs_set_memconf

On 24/01/15 22:28, Semen Protsenko wrote:
> Some GPMC_CONFIG7 register bits marked as "RESERVED", means they
> shouldn't be overwritten. A typical approach to handle such bits called
> "Read-Modify-Write". Writing procedure used in gpmc_cs_set_memconf()
> utilizes RMW technique, but implemented incorrectly. Due to obvious typo
> in code read register value is being rewritten by another value, which
> leads to loss of read RESERVED bits. This patch fixes this.
> 
> While at it, replace magic numbers with named constants to improve code
> readability.
> 
> Signed-off-by: Semen Protsenko <semen.protsenko@...ballogic.com>

This is much nicer.

Acked-by: Roger Quadros <rogerq@...com>

cheers,
-roger

> ---
>  drivers/memory/omap-gpmc.c |   20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/memory/omap-gpmc.c b/drivers/memory/omap-gpmc.c
> index 24696f5..10eb4ac 100644
> --- a/drivers/memory/omap-gpmc.c
> +++ b/drivers/memory/omap-gpmc.c
> @@ -153,6 +153,15 @@
>  #define GPMC_CONFIG1_FCLK_DIV4          (GPMC_CONFIG1_FCLK_DIV(3))
>  #define GPMC_CONFIG7_CSVALID		(1 << 6)
>  
> +#define GPMC_CONFIG7_BASEADDRESS_MASK	0x3f
> +#define GPMC_CONFIG7_CSVALID_MASK	BIT(6)
> +#define GPMC_CONFIG7_MASKADDRESS_OFFSET	8
> +#define GPMC_CONFIG7_MASKADDRESS_MASK	(0xf << GPMC_CONFIG7_MASKADDRESS_OFFSET)
> +/* All CONFIG7 bits except reserved bits */
> +#define GPMC_CONFIG7_MASK		(GPMC_CONFIG7_BASEADDRESS_MASK | \
> +					 GPMC_CONFIG7_CSVALID_MASK |     \
> +					 GPMC_CONFIG7_MASKADDRESS_MASK)
> +
>  #define GPMC_DEVICETYPE_NOR		0
>  #define GPMC_DEVICETYPE_NAND		2
>  #define GPMC_CONFIG_WRITEPROTECT	0x00000010
> @@ -586,12 +595,15 @@ static int gpmc_cs_set_memconf(int cs, u32 base, u32 size)
>  	if (base & (size - 1))
>  		return -EINVAL;
>  
> +	base >>= GPMC_CHUNK_SHIFT;
>  	mask = (1 << GPMC_SECTION_SHIFT) - size;
> +	mask >>= GPMC_CHUNK_SHIFT;
> +	mask <<= GPMC_CONFIG7_MASKADDRESS_OFFSET;
> +
>  	l = gpmc_cs_read_reg(cs, GPMC_CS_CONFIG7);
> -	l &= ~0x3f;
> -	l = (base >> GPMC_CHUNK_SHIFT) & 0x3f;
> -	l &= ~(0x0f << 8);
> -	l |= ((mask >> GPMC_CHUNK_SHIFT) & 0x0f) << 8;
> +	l &= ~GPMC_CONFIG7_MASK;
> +	l |= base & GPMC_CONFIG7_BASEADDRESS_MASK;
> +	l |= mask & GPMC_CONFIG7_MASKADDRESS_MASK;
>  	l |= GPMC_CONFIG7_CSVALID;
>  	gpmc_cs_write_reg(cs, GPMC_CS_CONFIG7, l);
>  
> 

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