problems with am335x_sdram_size()

[Sascha Hauer]

On Thu, Mar 01, 2018 at 03:23:33PM +0100, Giorgio Dal Molin wrote:
> Hi,
> 
> working with the TI AM335x Evaluation Module I noticed that the function
> am335x_sdram_size() always returns 0 instead of the computed sdram size.
> 
> I could trace back the problem to the fact that the function does its 
> computation based on the value of the register CM_EMIF_SDRAM_CONFIG
> (addr. 0x44e10110), but this register is not written to by the function
> am33xx_config_sdram() and just returns its initial value (0).
> The datasheet says CM_EMIF_SDRAM_CONFIG should have the same value as
> AM33XX_EMIF4_0_REG(SDRAM_CONFIG) (addr. 0x4c000008)

CM_EMIF_SDRAM_CONFIG is written when regs->zq_config is set and if it's
set then indeed the same value is written there as also written to
AM33XX_EMIF4_0_REG(SDRAM_CONFIG).

> 
> To conclude, to fix the problem with am335x_sdram_size() you can either
> use AM33XX_EMIF4_0_REG(SDRAM_CONFIG) instead of CM_EMIF_SDRAM_CONFIG
> in am335x_sdram_size().
> 
>  or
> 
> initialize CM_EMIF_SDRAM_CONFIG in am33xx_config_sdram() with the same value
> as AM33XX_EMIF4_0_REG(SDRAM_CONFIG) (regs->sdram_config)

I'm fine with either way. Maybe the datasheet gives us a hint which way
to choose? Why is CM_EMIF_SDRAM_CONFIG only written when regs->zq_config
is set? Is this correct?

Sascha

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