From: Fabrice Gasnier <fabrice.gasnier@st.com>
To: <jic23@kernel.org>
Cc: <linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <mcoquelin.stm32@gmail.com>,
<alexandre.torgue@st.com>, <fabrice.gasnier@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: [PATCH v2 1/8] iio: adc: stm32-dfsdm: make spi_master_freq more accurate
Date: Thu, 21 Mar 2019 17:47:22 +0100 [thread overview]
Message-ID: <1553186849-6261-2-git-send-email-fabrice.gasnier@st.com> (raw)
In-Reply-To: <1553186849-6261-1-git-send-email-fabrice.gasnier@st.com>
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>
---
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");
--
2.7.4
next prev parent reply other threads:[~2019-03-21 16:48 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 ` Fabrice Gasnier [this message]
2019-03-24 16:41 ` [PATCH v2 1/8] iio: adc: stm32-dfsdm: make spi_master_freq more accurate Jonathan Cameron
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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