linux-kernel - Re: [PATCH] drivers: mfd: ti_am335x_tscadc: increase ADC ref clock to 24MHz

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Date:   Mon, 24 Oct 2016 13:58:55 -0700
From:   John Syne <john3909@...il.com>
To:     Mugunthan V N <mugunthanvnm@...com>
Cc:     Lee Jones <lee.jones@...aro.org>, linux-iio@...r.kernel.org,
        Tony Lindgren <tony@...mide.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Vignesh R <vigneshr@...com>, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Sekhar Nori <nsekhar@...com>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [PATCH] drivers: mfd: ti_am335x_tscadc: increase ADC ref clock to 24MHz


> On Oct 23, 2016, at 11:02 PM, Mugunthan V N <mugunthanvnm@...com> wrote:
> 
> Increase ADC reference clock from 3MHz to 24MHz so that the
> sampling rates goes up from 100K samples per second to 800K
> samples per second on AM335x and AM437x SoC.
> 
> Also increase opendelay for touchscreen configuration to
> equalize the increase in ADC reference clock frequency,
> which results in the same amount touch events reported via
> evtest on AM335x GP EVM.
> 
> Signed-off-by: Mugunthan V N <mugunthanvnm@...com>
> ---
> 
> This patch depends on ADC DMA patch series [1]
> 
> Without DMA support, when ADC ref clock is set at 24MHz, I am
> seeing fifo overflow as CPU is not able to pull the ADC samples.
> This answers that DMA support is must for ADC to consume the
> samples generated at 24MHz with no open, step delay or
> averaging with patch [2].
> 
> Measured the performance with the iio_generic_buffer with the
> patch [3] applied
> 
> [1] - http://www.spinics.net/lists/devicetree/msg145045.html
> [2] - http://pastebin.ubuntu.com/23357935/
> [3] - http://pastebin.ubuntu.com/23357939/
> 
> ---
> include/linux/mfd/ti_am335x_tscadc.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mfd/ti_am335x_tscadc.h b/include/linux/mfd/ti_am335x_tscadc.h
> index b9a53e0..96c4207 100644
> --- a/include/linux/mfd/ti_am335x_tscadc.h
> +++ b/include/linux/mfd/ti_am335x_tscadc.h
> @@ -90,7 +90,7 @@
> /* Delay register */
> #define STEPDELAY_OPEN_MASK	(0x3FFFF << 0)
> #define STEPDELAY_OPEN(val)	((val) << 0)
> -#define STEPCONFIG_OPENDLY	STEPDELAY_OPEN(0x098)
Wouldn’t this be better to add this to the devicetree?

	ti,chan-step-avg = <0x16 0x16 0x16 0x16 0x16 0x16 0x16>;
	ti,chan-step-opendelay = <0x500 0x500 0x500 0x500 0x500 0x500 0x500>;
	ti,chan-step-sampledelay = <0x0 0x0 0x0 0x0 0x0 0x0 0x0>;

Regards,
John
> +#define STEPCONFIG_OPENDLY	STEPDELAY_OPEN(0x500)
> #define STEPDELAY_SAMPLE_MASK	(0xFF << 24)
> #define STEPDELAY_SAMPLE(val)	((val) << 24)
> #define STEPCONFIG_SAMPLEDLY	STEPDELAY_SAMPLE(0)
> @@ -137,7 +137,7 @@
> #define SEQ_STATUS BIT(5)
> #define CHARGE_STEP		0x11
> 
> -#define ADC_CLK			3000000
> +#define ADC_CLK			24000000
> #define TOTAL_STEPS		16
> #define TOTAL_CHANNELS		8
> #define FIFO1_THRESHOLD		19
> -- 
> 2.10.1.502.g6598894
>