From: Jonathan Cameron <jic23@kernel.org>
To: Fabrice Gasnier <fabrice.gasnier@st.com>
Cc: <linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <mcoquelin.stm32@gmail.com>,
<alexandre.torgue@st.com>, <linux-iio@vger.kernel.org>,
<lars@metafoo.de>, <knaack.h@gmx.de>, <pmeerw@pmeerw.net>,
<linux-stm32@st-md-mailman.stormreply.com>,
<arnaud.pouliquen@st.com>, <olivier.moysan@st.com>
Subject: Re: [PATCH v2 1/8] iio: adc: stm32-dfsdm: make spi_master_freq more accurate
Date: Sun, 24 Mar 2019 16:41:29 +0000 [thread overview]
Message-ID: <20190324164129.620bf216@archlinux> (raw)
In-Reply-To: <1553186849-6261-2-git-send-email-fabrice.gasnier@st.com>
On Thu, 21 Mar 2019 17:47:22 +0100
Fabrice Gasnier <fabrice.gasnier@st.com> wrote:
> Current ckout divider may be set to a value that makes ckout to exceed
> spi-max-frequency. Rather use lower value (e.g. round up divider when
> ckout isn't accurate).
>
> Also when the SPI clock isn't accurate, 'spi_master_freq' is filled in
> with expected frequency. Use computed value instead to be more accurate:
> - e.g. source clock / (CKOUTDIV + 1)
>
> Enforce checks on the divider: ckoutdiv range can be from 1-255 to provide
> divider of 2-256.
>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Applied to the togreg branch of iio.git and pushed out as testing for the
autobuilders to play with it.
Thanks,
Jonathan
> ---
> Changes in v2:
> - rework the way to determine ckoutdiv bitfield: deal with divider directly
> to explicitly handle the rounding, the range constraints of 2-256 and the
> divider = ckoutdiv + 1.
> ---
> drivers/iio/adc/stm32-dfsdm-core.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/iio/adc/stm32-dfsdm-core.c b/drivers/iio/adc/stm32-dfsdm-core.c
> index bf089f5..472b809 100644
> --- a/drivers/iio/adc/stm32-dfsdm-core.c
> +++ b/drivers/iio/adc/stm32-dfsdm-core.c
> @@ -199,7 +199,7 @@ static int stm32_dfsdm_parse_of(struct platform_device *pdev,
> {
> struct device_node *node = pdev->dev.of_node;
> struct resource *res;
> - unsigned long clk_freq;
> + unsigned long clk_freq, divider;
> unsigned int spi_freq, rem;
> int ret;
>
> @@ -243,13 +243,20 @@ static int stm32_dfsdm_parse_of(struct platform_device *pdev,
> return 0;
> }
>
> - priv->spi_clk_out_div = div_u64_rem(clk_freq, spi_freq, &rem) - 1;
> - if (!priv->spi_clk_out_div) {
> - /* spi_clk_out_div == 0 means ckout is OFF */
> + divider = div_u64_rem(clk_freq, spi_freq, &rem);
> + /* Round up divider when ckout isn't precise, not to exceed spi_freq */
> + if (rem)
> + divider++;
> +
> + /* programmable divider is in range of [2:256] */
> + if (divider < 2 || divider > 256) {
> dev_err(&pdev->dev, "spi-max-frequency not achievable\n");
> return -EINVAL;
> }
> - priv->dfsdm.spi_master_freq = spi_freq;
> +
> + /* SPI clock output divider is: divider = CKOUTDIV + 1 */
> + priv->spi_clk_out_div = divider - 1;
> + priv->dfsdm.spi_master_freq = clk_freq / (priv->spi_clk_out_div + 1);
>
> if (rem) {
> dev_warn(&pdev->dev, "SPI clock not accurate\n");
next prev parent reply other threads:[~2019-03-24 16:41 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-21 16:47 [PATCH v2 0/8] iio: adc: stm32-dfsdm: add buffer modes Fabrice Gasnier
2019-03-21 16:47 ` [PATCH v2 1/8] iio: adc: stm32-dfsdm: make spi_master_freq more accurate Fabrice Gasnier
2019-03-24 16:41 ` Jonathan Cameron [this message]
2019-03-21 16:47 ` [PATCH v2 2/8] iio: adc: stm32-dfsdm: continuous mode depends on current mode Fabrice Gasnier
2019-03-24 16:43 ` Jonathan Cameron
2019-03-21 16:47 ` [PATCH v2 3/8] iio: adc: stm32-dfsdm: move dma enable from start_conv() to start_dma() Fabrice Gasnier
2019-03-24 16:44 ` Jonathan Cameron
2019-03-21 16:47 ` [PATCH v2 4/8] iio: adc: stm32-dfsdm: move dma slave config to start routine Fabrice Gasnier
2019-03-24 16:45 ` Jonathan Cameron
2019-03-21 16:47 ` [PATCH v2 5/8] iio: adc: stm32-dfsdm: enable hw consumer Fabrice Gasnier
2019-03-24 16:45 ` Jonathan Cameron
2019-03-21 16:47 ` [PATCH v2 6/8] iio: adc: stm32-dfsdm: add support for scan mode Fabrice Gasnier
2019-03-24 16:46 ` Jonathan Cameron
2019-03-21 16:47 ` [PATCH v2 7/8] iio: adc: stm32-dfsdm: add support for buffer modes Fabrice Gasnier
2019-03-24 17:11 ` Jonathan Cameron
2019-03-21 16:47 ` [PATCH v2 8/8] iio: adc: stm32-dfsdm: claim direct mode for raw read and settings Fabrice Gasnier
2019-03-24 17:12 ` Jonathan Cameron
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