linux-kernel - Re: [PATCH 3/3] ARM: OMAP2+: gpmc: Do not modify LIMITEDADDRESS on new architectures

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Message-ID: <54C60DF1.9070300@ti.com>
Date:	Mon, 26 Jan 2015 11:50:41 +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 3/3] ARM: OMAP2+: gpmc: Do not modify LIMITEDADDRESS on
 new architectures

Hi,

On 24/01/15 22:28, Semen Protsenko wrote:
> New OMAP-based architectures (like OMAP5, DRA7XX, AM572X) don't have
> LIMITEDADDRESS bit in GPMC_CONFIG register (this bit marked as
> RESERVED). Seems like these SoCs have new revision of GPMC IP-core
> (despite of same GPMC_REVISION value as for earlier SoCs).
> 
> According to OMAP5 TRM: "Nonmultiplexed NOR flash devices are
> supported by the GPMC, but their use is highly limited. Because only
> 10 address pins are available on the GPMC interface, the maximum device
> size supported is 2KiB."
> 
> From [1]:
>  - OMAP4 GPMC_CONFIG has LIMITEDADDRESS bit, hence supports both
>    limited and full address mode.
>  - OMAP5 GPMC_CONFIG doesn't have LIMITEDDADDRESS bit.

According to OMAP5432 TRM SWPU249AC, I can see LIMITEDADDRESS bit in GPMC_CONFIG.
Which TRM version are you referring to?

>    OMAP5 supports only limited address mode for nonmultiplexed flashes
>    In this mode only A1-A10 lines are being modified by GPMC, which
>    leaves us (on flash devices with 1 word = 2 bytes) only
>    2^10 * 2 = 2KiB memory that we can access.
>  - DRA7XX GPMC_CONFIG doesn't have LIMITEDADDRESS bit.
>    DRA7XX supports only full address mode for nonmultiplexed flashes
>    (current TRM says contrary, but according to [1] it's typo and
>    gonna be fixed in new DRA7XX TRMs). In full address mode all
>    A1-A26 lines are modified by GPMC, so one can address up to 128 MiB.
> 
> This patch ensures that GPMC driver doesn't try to modify LIMITEDADDRESS
> bit on new OMAP-based devices, because such an action could possibly
> lead to undefined behavior in GPMC state-machine (this bit is marked as
> RESERVED now).
> 
> [1] http://e2e.ti.com/support/omap/f/885/t/396939
> 
> Signed-off-by: Semen Protsenko <semen.protsenko@...ballogic.com>
> ---
>  drivers/memory/omap-gpmc.c |   32 ++++++++++++++++++++++++--------
>  1 file changed, 24 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/memory/omap-gpmc.c b/drivers/memory/omap-gpmc.c
> index db77adb..477d0ba 100644
> --- a/drivers/memory/omap-gpmc.c
> +++ b/drivers/memory/omap-gpmc.c
> @@ -108,6 +108,7 @@
>  #define	GPMC_HAS_WR_ACCESS		0x1
>  #define	GPMC_HAS_WR_DATA_MUX_BUS	0x2
>  #define	GPMC_HAS_MUX_AAD		0x4
> +#define	GPMC_HAS_LIMITEDADDRESS		0x8
>  
>  #define GPMC_NR_WAITPINS		4
>  
> @@ -1709,6 +1710,18 @@ static int gpmc_probe_onenand_child(struct platform_device *pdev,
>  }
>  #endif
>  
> +static void gpmc_disable_limited(void)
> +{
> +	if (gpmc_capability & GPMC_HAS_LIMITEDADDRESS) {
> +		u32 val;
> +
> +		/* Clear limited address i.e. enable A26-A11 */
> +		val = gpmc_read_reg(GPMC_CONFIG);
> +		val &= ~GPMC_CONFIG_LIMITEDADDRESS;
> +		gpmc_write_reg(GPMC_CONFIG, val);
> +	}
> +}
> +
>  /**
>   * gpmc_probe_generic_child - configures the gpmc for a child device
>   * @pdev:	pointer to gpmc platform device
> @@ -1726,7 +1739,6 @@ static int gpmc_probe_generic_child(struct platform_device *pdev,
>  	unsigned long base;
>  	const char *name;
>  	int ret, cs;
> -	u32 val;
>  
>  	if (of_property_read_u32(child, "reg", &cs) < 0) {
>  		dev_err(&pdev->dev, "%s has no 'reg' property\n",
> @@ -1805,10 +1817,7 @@ static int gpmc_probe_generic_child(struct platform_device *pdev,
>  		goto err;
>  	}
>  
> -	/* Clear limited address i.e. enable A26-A11 */
> -	val = gpmc_read_reg(GPMC_CONFIG);
> -	val &= ~GPMC_CONFIG_LIMITEDADDRESS;
> -	gpmc_write_reg(GPMC_CONFIG, val);
> +	gpmc_disable_limited();
>  
>  	/* Enable CS region */
>  	gpmc_cs_enable_mem(cs);
> @@ -1935,14 +1944,21 @@ static int gpmc_probe(struct platform_device *pdev)
>  	 * devices support the addr-addr-data multiplex protocol.
>  	 *
>  	 * GPMC IP revisions:
> -	 * - OMAP24xx			= 2.0
> -	 * - OMAP3xxx			= 5.0
> -	 * - OMAP44xx/54xx/AM335x	= 6.0
> +	 * - OMAP24xx				= 2.0
> +	 * - OMAP3xxx				= 5.0
> +	 * - OMAP44xx/54xx/AM335x/DRA7XX	= 6.0
>  	 */
>  	if (GPMC_REVISION_MAJOR(l) > 0x4)
>  		gpmc_capability = GPMC_HAS_WR_ACCESS | GPMC_HAS_WR_DATA_MUX_BUS;
>  	if (GPMC_REVISION_MAJOR(l) > 0x5)
>  		gpmc_capability |= GPMC_HAS_MUX_AAD;
> +	if (GPMC_REVISION_MAJOR(l) < 0x6)
> +		gpmc_capability |= GPMC_HAS_LIMITEDADDRESS;
> +#if !defined(CONFIG_SOC_OMAP5) && !defined(CONFIG_SOC_DRA7XX)
> +	if (GPMC_REVISION_MAJOR(l) == 0x6)
> +		gpmc_capability |= GPMC_HAS_LIMITEDADDRESS;
> +#endif
> +

This logic will prevent GPMC_HAS_LIMITEDADDRESS to be set on OMAP4 if we have
either SOC_OMAP5 or SOC_DRA7XX enabled. So it is not good.

I think this patch is unnecessary as we are only setting the reserved bit to 0.
It is safe to set RESERVED bit to 0. We are not modifying it as RESERVED bit is
meant to be 0. If bootloader is setting the reserved bit to 1, it is a bug in
the bootloader.

>  	dev_info(gpmc_dev, "GPMC revision %d.%d\n", GPMC_REVISION_MAJOR(l),
>  		 GPMC_REVISION_MINOR(l));
>  
> 

cheers,
-roger
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