linux-kernel - Re: [PATCH 2/2] clk: rockchip: fix the rk3399 sdmmc sample shift

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Message-ID: <20160512231023.GA63308@google.com>
Date:	Thu, 12 May 2016 16:10:23 -0700
From:	Brian Norris <briannorris@...omium.org>
To:	Douglas Anderson <dianders@...omium.org>
Cc:	Heiko Stuebner <heiko@...ech.de>, mturquette@...libre.com,
	sboyd@...eaurora.org, zhengxing@...k-chips.com,
	shawn.lin@...k-chips.com, linux-kernel@...r.kernel.org,
	linux-rockchip@...ts.infradead.org, linux-clk@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] clk: rockchip: fix the rk3399 sdmmc sample shift

On Thu, May 12, 2016 at 11:03:17AM -0700, Doug Anderson wrote:
> Just like every other Rockhip device, the MMC "_sample" clocks should
> have a shift of 0, not a shift of 1.  The rk3399 TRM agrees.  Presumably
> these values were set to 0 because of a typo.

I'll semi-disagree about the TRM: the TRM doesn't seem to agree with
itself, so it sometimes agrees with you and sometimes doesn't :)

On page 79 of the 2nd (?) book, it looks like {SDMMC,SDIO}_CON{0,}[2:1]
are {drv,sample}_degree. But on page 208 of the 1st book, those are put
at bits [1:0].

Perhaps we can get a straight answer from Rockchip though.

Brian

> Things _sorta_ would have worked with the incorrect sample phase shift
> because of the register layout but wouldn't have been ideal and we would
> have skipped lots of phases.  Also: we would never actually enabled the
> fine delay unless we happened to have 128 or more delay elements.
> 
> This is expected behavior before this patch:
> * Try to set:     0 degrees +   1 delay elements
>   Actually get:   0 degrees +   0 delay elements
> * Try to set:    90 degrees +   0 delay elements
>   Actually get: 180 degrees +   0 delay elements
> * Try to set:   180 degrees +   0 delay elements
>   Actually get:   0 degrees +   0 delay elements
> * Try to set:   270 degrees +   0 delay elements
>   Actually get: 180 degrees +   0 delay elements
> * Try to set:     0 degrees + 129 delay elements
>   Actually get:   0 degrees +   2 delay elements
> * Try to set:   180 degrees + 129 delay elements
>   Actually get:   0 degrees +   3 delay elements
> * Try to set:     0 degrees + 130 delay elements
>   Actually get:   0 degrees +   4 delay elements
> 
> I verified that old code had a problem by turning on debug printouts and
> seeing that the old code would report this for one SD card I had:
>   Good phase range 347-101 (115 len)
>   Good phase range 202-326 (125 len)
> 
> After my fix, it went down to one big good range for the same card.
> This is more expected:
>   Good phase range 189-1 (173 len)
>   Good phase range 82-85 (4 len)
>   Good phase range 166-168 (3 len)
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>  drivers/clk/rockchip/clk-rk3399.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/rockchip/clk-rk3399.c b/drivers/clk/rockchip/clk-rk3399.c
> index 291543f52caa..14ff3e109e1e 100644
> --- a/drivers/clk/rockchip/clk-rk3399.c
> +++ b/drivers/clk/rockchip/clk-rk3399.c
> @@ -895,10 +895,10 @@ static struct rockchip_clk_branch rk3399_clk_branches[] __initdata = {
>  			RK3399_CLKGATE_CON(6), 1, GFLAGS),
>  
>  	MMC(SCLK_SDMMC_DRV,     "sdmmc_drv",    "clk_sdmmc", RK3399_SDMMC_CON0, 1),
> -	MMC(SCLK_SDMMC_SAMPLE,  "sdmmc_sample", "clk_sdmmc", RK3399_SDMMC_CON1, 1),
> +	MMC(SCLK_SDMMC_SAMPLE,  "sdmmc_sample", "clk_sdmmc", RK3399_SDMMC_CON1, 0),
>  
>  	MMC(SCLK_SDIO_DRV,      "sdio_drv",    "clk_sdio",  RK3399_SDIO_CON0,  1),
> -	MMC(SCLK_SDIO_SAMPLE,   "sdio_sample", "clk_sdio",  RK3399_SDIO_CON1,  1),
> +	MMC(SCLK_SDIO_SAMPLE,   "sdio_sample", "clk_sdio",  RK3399_SDIO_CON1,  0),
>  
>  	/* pcie */
>  	COMPOSITE(SCLK_PCIE_PM, "clk_pcie_pm", mux_pll_src_cpll_gpll_npll_24m_p, 0,