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[spi_flash] handle reentrance gracefully #4397

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Mar 23, 2021
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[spi_flash] handle reentrance gracefully #4397

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24 changes: 16 additions & 8 deletions supervisor/shared/external_flash/spi_flash.c
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Original file line number Diff line number Diff line change
Expand Up @@ -42,10 +42,12 @@ const external_flash_device *flash_device;
uint32_t spi_flash_baudrate;

// Enable the flash over SPI.
static void flash_enable(void) {
while (!common_hal_busio_spi_try_lock(&supervisor_flash_spi_bus)) {
static bool flash_enable(void) {
if (common_hal_busio_spi_try_lock(&supervisor_flash_spi_bus)) {
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Is it worth retrying X amount of times even? I know adafruit_bus_device had a routine to catch background tasks and keep trying for the lock, I'm not familiar enough to say for sure this needs it just a thought.

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Could it be that instead of the busy-wait in https://github.com/adafruit/Adafruit_CircuitPython_BusDevice/blob/master/adafruit_bus_device/spi_device.py#L73, it's better to throw an exception when the SPI is locked? Then the user would have control over how many times, if at all, to retry.

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Looping over common_hal_busio_spi_try_lock() in C will not succeed if it doesn't work the first time: If foreground Python code has locked the bus, it has to be able to proceed in order to unlock the bus. I don't think we ever un/lock the bus from an interrupt context.

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@jepler doesn't the same apply to adafruit_bus_device? Or may run_background_tasks() lock SPI in one tick, and unlock it in another?

common_hal_digitalio_digitalinout_set_value(&cs_pin, false);
return true;
}
common_hal_digitalio_digitalinout_set_value(&cs_pin, false);
return false;
}

// Disable the flash over SPI.
Expand All @@ -54,8 +56,10 @@ static void flash_disable(void) {
common_hal_busio_spi_unlock(&supervisor_flash_spi_bus);
}

static bool transfer(uint8_t *command, uint32_t command_length, uint8_t *data_in, uint8_t *data_out, uint32_t data_length) {
flash_enable();
static bool transfer(uint8_t* command, uint32_t command_length, uint8_t* data_in, uint8_t* data_out, uint32_t data_length) {
if (!flash_enable()) {
return false;
}
bool status = common_hal_busio_spi_write(&supervisor_flash_spi_bus, command, command_length);
if (status) {
if (data_in != NULL && data_out != NULL) {
Expand Down Expand Up @@ -103,7 +107,9 @@ bool spi_flash_write_data(uint32_t address, uint8_t *data, uint32_t data_length)
uint8_t request[4] = {CMD_PAGE_PROGRAM, 0x00, 0x00, 0x00};
// Write the SPI flash write address into the bytes following the command byte.
address_to_bytes(address, request + 1);
flash_enable();
if (!flash_enable()) {
return false;
}
common_hal_busio_spi_configure(&supervisor_flash_spi_bus, spi_flash_baudrate, 0, 0, 8);
bool status = common_hal_busio_spi_write(&supervisor_flash_spi_bus, request, 4);
if (status) {
Expand All @@ -120,9 +126,11 @@ bool spi_flash_read_data(uint32_t address, uint8_t *data, uint32_t data_length)
request[0] = CMD_FAST_READ_DATA;
command_length = 5;
}
// Write the SPI flash write address into the bytes following the command byte.
// Write the SPI flash read address into the bytes following the command byte.
address_to_bytes(address, request + 1);
flash_enable();
if (!flash_enable()) {
return false;
}
common_hal_busio_spi_configure(&supervisor_flash_spi_bus, spi_flash_baudrate, 0, 0, 8);
bool status = common_hal_busio_spi_write(&supervisor_flash_spi_bus, request, command_length);
if (status) {
Expand Down