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can: mcp25xxfd: mcp25xxfd_probe(): add SPI clk limit related errata information 

This patch adds a reference to the recent released MCP2517FD and MCP2518FD
errata sheets and paste the explanation.

The driver already implements the proposed fix.

Signed-off-by: Thomas Kopp <thomas.kopp@microchip.com>
Link: https://lore.kernel.org/r/20200925065606.358-1-thomas.kopp@microchip.com
[mkl: split into two patches, adjust subject and commit message]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
Thomas Kopp 2020-09-25 08:56:06 +02:00 committed by Marc Kleine-Budde
parent 788b83ea2c
commit f5b84dedf7
1 changed files with 14 additions and 5 deletions
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19
drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c
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@ -2819,11 +2819,21 @@ static int mcp25xxfd_probe(struct spi_device *spi)
priv->devtype_data = *(struct mcp25xxfd_devtype_data *)
spi_get_device_id(spi)->driver_data;
/* According to the datasheet the SPI clock must be less or
* equal SYSCLOCK / 2.
/* Errata Reference:
* mcp2517fd: DS80000789B, mcp2518fd: DS80000792C 4.
*
* It turns out, that the Controller is not stable at this
* rate. Known good and bad combinations are:
* The SPI can write corrupted data to the RAM at fast SPI
* speeds:
*
* Simultaneous activity on the CAN bus while writing data to
* RAM via the SPI interface, with high SCK frequency, can
* lead to corrupted data being written to RAM.
*
* Fix/Work Around:
* Ensure that FSCK is less than or equal to 0.85 *
* (FSYSCLK/2).
*
* Known good and bad combinations are:
*
* MCP ext-clk SoC SPI SPI-clk max-clk parent-clk Status config
*
@ -2836,7 +2846,6 @@ static int mcp25xxfd_probe(struct spi_device *spi)
* 2517 40 MHz atmel,sama5d27 atmel,at91rm9200-spi 16400000 Hz 82.00% 82000000 Hz good default
* 2518 40 MHz atmel,sama5d27 atmel,at91rm9200-spi 16400000 Hz 82.00% 82000000 Hz good default
*
* Limit SPI clock to 85% of SYSCLOCK / 2 for now.
*/
priv->spi_max_speed_hz_orig = spi->max_speed_hz;
spi->max_speed_hz = min(spi->max_speed_hz, freq / 2 / 1000 * 850);