* [PATCH 1/1] spi: pxa2xx: Enable SSP controller for CS toggle
[not found] ` <20200218134906.25458-1-shobhit.srivastava-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
@ 2020-02-18 13:49 ` Shobhit Srivastava
2020-02-18 13:50 ` [PATCH 0/1] " Mark Brown
1 sibling, 0 replies; 3+ messages in thread
From: Shobhit Srivastava @ 2020-02-18 13:49 UTC (permalink / raw)
To: daniel-cYrQPVfZoowdnm+yROfE0A,
haojian.zhuang-Re5JQEeQqe8AvxtiuMwx3w,
robert.jarzmik-GANU6spQydw, broonie-DgEjT+Ai2ygdnm+yROfE0A,
linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r,
linux-spi-u79uwXL29TY76Z2rM5mHXA,
linux-kernel-u79uwXL29TY76Z2rM5mHXA
Cc: furquan-hpIqsD4AKlfQT0dZR+AlfA, rajatja-hpIqsD4AKlfQT0dZR+AlfA,
evgreen-hpIqsD4AKlfQT0dZR+AlfA,
andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA
In some circumstances on Intel LPSS controllers, toggling the LPSS
CS control register doesn't actually cause the CS line to toggle.
This ruins SPI transactions that either rely on delay_usecs,
or toggle the CS line without sending any data.
This seems to be because the SSP controller is in disabled state.
As per the spec, the controller needs to be enabled for CS change
to take effect.
This issue is not seen in cases where there is data to be
transferred because then the SSCR0 gets enabled via
pxa2xx_configure_sscr0().
Signed-off-by: Shobhit Srivastava <shobhit.srivastava-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
drivers/spi/spi-pxa2xx.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index 4c7a71f0fb3e..414afc72ef44 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -370,7 +370,7 @@ static void lpss_ssp_cs_control(struct spi_device *spi, bool enable)
struct driver_data *drv_data =
spi_controller_get_devdata(spi->controller);
const struct lpss_config *config;
- u32 value;
+ u32 value, sscr0;
config = lpss_get_config(drv_data);
@@ -382,7 +382,18 @@ static void lpss_ssp_cs_control(struct spi_device *spi, bool enable)
value &= ~LPSS_CS_CONTROL_CS_HIGH;
else
value |= LPSS_CS_CONTROL_CS_HIGH;
+
+ /* To propagate CS value to output, the controller should
+ * be enabled. This is needed for devices that just do
+ * CS assert, wait and CS deassert without sending any data.
+ */
+ sscr0 = pxa2xx_spi_read(drv_data, SSCR0);
+ pxa2xx_spi_write(drv_data, SSCR0, sscr0 | SSCR0_SSE);
+
__lpss_ssp_write_priv(drv_data, config->reg_cs_ctrl, value);
+
+ /* Restore the original SSCR0 config*/
+ pxa2xx_spi_write(drv_data, SSCR0, sscr0);
}
static void cs_assert(struct spi_device *spi)
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH 0/1] Enable SSP controller for CS toggle
[not found] ` <20200218134906.25458-1-shobhit.srivastava-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2020-02-18 13:49 ` [PATCH 1/1] spi: pxa2xx: " Shobhit Srivastava
@ 2020-02-18 13:50 ` Mark Brown
1 sibling, 0 replies; 3+ messages in thread
From: Mark Brown @ 2020-02-18 13:50 UTC (permalink / raw)
To: Shobhit Srivastava
Cc: daniel-cYrQPVfZoowdnm+yROfE0A,
haojian.zhuang-Re5JQEeQqe8AvxtiuMwx3w,
robert.jarzmik-GANU6spQydw,
linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r,
linux-spi-u79uwXL29TY76Z2rM5mHXA,
linux-kernel-u79uwXL29TY76Z2rM5mHXA,
furquan-hpIqsD4AKlfQT0dZR+AlfA, rajatja-hpIqsD4AKlfQT0dZR+AlfA,
evgreen-hpIqsD4AKlfQT0dZR+AlfA,
andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA
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On Tue, Feb 18, 2020 at 07:19:05PM +0530, Shobhit Srivastava wrote:
>
> SPI CS assert may not always be accompanied by data. There are cases
> where we want to assert CS, wait and then deassert CS. There is no
> clocking or reading required. On Intel CNL LPSS controller, it was
Please don't send cover letters for single patches, if there is anything
that needs saying put it in the changelog of the patch or after the ---
if it's administrative stuff. This reduces mail volume and ensures that
any important information is recorded in the changelog rather than being
lost.
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^ permalink raw reply [flat|nested] 3+ messages in thread