SPI Clock Polarity not changing

aravindchakrava — Mon, 13 Sep 2021 09:02:12 GMT

Hi All,

We are using iMX8M Mini based custom board. We have loaded Linux (using uBoot + Yocto) whose Kernel version is 4.14.98-2.2.0.

We are have written SPI driver for ecSPI3. We would like to use SPI in Mode 3 (i.e., CPOL = CPOH = 1).

Following are the parameters we are using

void init_eeprom_spi(void) { strcpy(eeprom_spiconfig.spi_device, SPI_EEPROM_DEVICE); eeprom_spiconfig.spi_bits = 8; eeprom_spiconfig.spi_mode = 0x03;//SPI_EEPROM_MODE; eeprom_spiconfig.spi_speed = 4000000;//SPI_SPEED_6MHZ; /*5 MHz */ eeprom_spiconfig.spi_tx_buffer = (char *)spi_eeprom_txbuffer; eeprom_spiconfig.spi_rx_buffer = (char *)spi_eeprom_rxbuffer; eeprom_spiconfig.spi_buffsz = SPI_BUFFER_MAX_SIZE; eeprom_spiconfig.spi_fd = -1; }

And here is the code were we are writing the data to SPI driver

int spi_transfer(struct spi_eeprom_conf *conf, char *txBuff, char *rxBuff, int size, int endian) { int ret; void *txptr, *rxptr; txptr = (void *)txBuff; rxptr = (void *)rxBuff; /* Check endianess and swap if necessary*/ if (endian == SPI_BIG_ENDIAN) for (int i = 0; i < (size/M_FOUR); i ++) SwapEndian((uint32_t *)txptr + i); /* Was not getting proper clock polarity, hence adding CPOL, CPOH init here */ /* Set read mode */ if ((ret = ioctl(conf->spi_fd, SPI_IOC_RD_MODE, &conf->spi_mode)) < M_ZERO) { printdbg(("\n spi_open: set read mode failed")); close(conf->spi_fd); return M_INVALID; } printdbg(("\n spi_open: set read mode successfull")); /* Set write mode */ if ((ret = ioctl(conf->spi_fd, SPI_IOC_WR_MODE, &conf->spi_mode)) < M_ZERO) { printdbg(("\n spi_open: set write mode failed")); close(conf->spi_fd); return M_INVALID; } printdbg(("\n spi_open: set wrie mode successfull")); /* Initialize transfer structure for SPI linux API */ struct spi_ioc_transfer tr = { .tx_buf = (unsigned long)(char *)txBuff, .rx_buf = (unsigned long)(char *)rxBuff, .len = size, .delay_usecs = conf->spi_delay, .speed_hz = conf->spi_speed, .bits_per_word = conf->spi_bits, }; /* Initiate SPI transfer */ if ((ret = ioctl(conf->spi_fd, SPI_IOC_MESSAGE(1), &tr)) < M_ZERO) { printdbg(("\n spi_transfer: transfer failed")); return M_INVALID; } /* Check endianess and swap bytes if necessary */ if (endian == SPI_BIG_ENDIAN) for (int i = 0; i < (size/M_FOUR); i ++) SwapEndian((uint32_t *)rxptr + i); printdbg(("\n spi_transfer: transfer success [Size = %d bytes]", ret)); /* Return no of bytes trasnferred */ return ret; }

In-spite of all the trials, I am not able to change the mode of SPI. It is stuck with "CLOCK being Low in Idle". Interestingly, I can manipulate clock frequency without any problem. I am able to get the data out from MOSI also.

Can some one guide me how to change SPI mode? Do you see any problem in code?

Regards,

Aravind

Re: SPI Clock Polarity not changing

igorpadykov — Mon, 13 Sep 2021 10:49:46 GMT

Hi Aravind

for clock polarity one can look at "MX51_ECSPI_CONFIG_SCLKPOL" in function mx51_ecspi_prepare_message() spi driver spi-imx.c

https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/spi/spi-imx.c?h=lf-5.10.y

Best regards
igor

Re: SPI Clock Polarity not changing

aravindchakrava — Mon, 20 Sep 2021 09:06:25 GMT

HI Igor,

Thank you for your reply. I did go through the SPI device driver code. However, I felt it is beyond my capability.

I am actually looking something which modifiable in user space not at kernel/driver level.

Thank you,

Aravind

Re: SPI Clock Polarity not changing

igorpadykov — Tue, 21 Sep 2021 06:42:07 GMT

one can try to debug it to find reason why polarity change is not happening,

read SCLK_PHA field register ECSPIx_CONFIGREG, use

AN4553 Using Open Source Debugging Tools for Linux on i.MX Processors
https://www.nxp.com/docs/en/application-note/AN4553.pdf

or memtool

https://source.codeaurora.org/external/imx/imx-test/tree/test/memtool?h=lf-5.10.y_2.0.0

Best regards
igor

Re: SPI Clock Polarity not changing

aravindchakrava — Wed, 22 Sep 2021 08:57:12 GMT

Hi Igor,

This is nice way of debugging within Linux. I will check.

Thank you very much.

Regards,

Aravind

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