[rtl872x] hal: fix issue that uart rx dma may hang up.

[XuGuohui]

Problem

When running the Serial2 stress test app as attached below, device may hang up over time.

Solution

1. Implement recursive TX/RX lock
2. Fix minor bug in ring buffer
3. Do not suspend DMA unless necessary.

Steps to Test

Build and run the below test app.

Example App

#include "Particle.h"

SYSTEM_MODE(MANUAL);
SYSTEM_THREAD(ENABLED);

Serial1LogHandler log(115200, LOG_LEVEL_ALL, {
    {"system", LOG_LEVEL_WARN}
});

constexpr uint16_t buffLen = 64;
uint8_t txBuff[buffLen];
uint8_t rxBuff[buffLen] = {};

system_tick_t was = 0;

void setup() {
    Serial2.begin(115200);
    for (int i = 0; i < buffLen; i++) {
        txBuff[i] = (uint8_t)i;
    }
    was = millis();
}

bool done = true;
size_t txLen = 0;
size_t rxCnt = 0;

void loop() {
    if (done) {
        txLen = random(1, buffLen);
        txLen = Serial2.write(txBuff, txLen);
        Log.printf("TX Done: %d\r\n", txLen);
        done = false;
        was = millis();
        rxCnt = 0;
    }

    size_t len = Serial2.available();
    if (len) {
        while (len--) {
            rxBuff[rxCnt] = Serial2.read();
            Log.printf("%02d ", rxBuff[rxCnt]);
            rxCnt++;
        }
    }

    if (millis() - was > 800) {
        was = millis();
        Log.printf("Done \r\n");
        done = true;
        if (rxCnt == txLen && !memcmp(txBuff, rxBuff, txLen)) {
            Log.info("Test Passed! len: %d", rxCnt);
        } else {
            Log.info("Test Failed! TX: %d, RX: %d", txLen, rxCnt);
            Serial2.breakTx();
            while (1);
        }
    }
}

References

N/A

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Completeness

• [x] User is totes amazing for contributing!
• [x] Contributor has signed CLA (Info here)
• [x] Problem and Solution clearly stated
• [ ] Run unit/integration/application tests on device
• [ ] Added documentation
• [ ] Added to CHANGELOG.md after merging (add links to docs and issues)