[U-Boot] [PATCH V3 5/9] EXYNOS5: DWMMC: API to set mmc clock divisor

From: Jaehoon Chung <jh80.chung@samsung.com>
To: u-boot@lists.denx.de
Subject: [U-Boot] [PATCH V3 5/9] EXYNOS5: DWMMC: API to set mmc clock divisor
Date: Thu, 03 Jan 2013 15:45:38 +0900	[thread overview]
Message-ID: <50E52912.1010409@samsung.com> (raw)
In-Reply-To: <CAPbRUmk6rNuTkWjf2fv=DoTqGdo+XXHDeBF-pC=rJU7qROoKbg@mail.gmail.com>

Hi Amar,

..snip..
>> I didn't understand this function(exynos5_mmc_set_clk_div?).
>> What purpose? I think good that proper to use the "div" as argument.
>> void exynos5_mmc_set_clk(int dev_id, unsigned int div).
> 
> 
> For fixing dwmmc driver, I referred to working code from
> "chromiumos/src/third_party/u-boot".
> In chromium uboot, during mhci init, the function "clock_set_mshci()" is
> called which is in "arch/arm/cpu/armv7/exynos5/clock.c"
> 
> Our function "*exynos5_mmc_set_clk_div()"* is same as "*clock_set_mshci()".*
> 
> Now coming to 'div' as argument .... we have the below scenarios / questions
> 1-> What is the value of 'div' to be passed from calling function ?
It will be the pre_ratio's value for FSYSx register.

> 2-> The value of 'div' needs to be computed in calling function.
It will be computed before called this function. For example, in dw_mmc.c or exynos_dw_mc.c

> 3-> As per my understanding, 'div' value depends on values of MPLL clock
> and FSYS1/2.
Right..but it will be changed the source clock. MMC/SD can use the every source clock.

> 4-> *Question:* Is it OK to put the piece of code which accesses MPLL,
> FSYS1, FSYS2 in drivers/mmc/exynos_dw_mmc.c. ?
Sure..we can use the get_mmc_clk/set_mmc_clk. then we can get source clock value.
and compute the div value for request clock.

> 5-> If we compute 'div' value in "drivers/mmc/exynos_dw_mmc.c", then
> there will be duplication of code (Read of FSYS1/2).
What code is duplication? Could you explain to me more?
Only need to compute the div value in exynos_dw_mmc.c.
why need to compute into here?

Best Regards,
Jaehoon Chung
> 
> Please comment on the above.
> 
>> +
>>  /* get_lcd_clk: return lcd clock frequency */
>>  static unsigned long exynos4_get_lcd_clk(void)
>>  {
>> diff --git a/arch/arm/include/asm/arch-exynos/clk.h
> b/arch/arm/include/asm/arch-exynos/clk.h
>> index 1935b0b..2fd7c3e 100644
>> --- a/arch/arm/include/asm/arch-exynos/clk.h
>> +++ b/arch/arm/include/asm/arch-exynos/clk.h
>> @@ -29,6 +29,9 @@
>>  #define VPLL 4
>>  #define BPLL 5
>>
>> +#define FSYS1_MMC0_DIV_MASK  0xff0f
>> +#define FSYS1_MMC0_DIV_VAL   0x0701
>> +
>>  unsigned long get_pll_clk(int pllreg);
>>  unsigned long get_arm_clk(void);
>>  unsigned long get_i2c_clk(void);
>> @@ -36,6 +39,7 @@ unsigned long get_pwm_clk(void);
>>  unsigned long get_uart_clk(int dev_index);
>>  unsigned long get_mmc_clk(int dev_index);
>>  void set_mmc_clk(int dev_index, unsigned int div);
>> +int exynos5_mmc_set_clk_div(int dev_index);
>>  unsigned long get_lcd_clk(void);
>>  void set_lcd_clk(void);
>>  void set_mipi_clk(void);
>>
> 
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