FROMLIST: serial: qcom_geni: Fix RX DMA stall when SE_DMA_RX_LEN_IN is zero

[vdadhani]

In qcom_geni_serial_handle_rx_dma(), geni_se_rx_dma_unprep() clears port->rx_dma_addr before SE_DMA_RX_LEN_IN is read. If the register is zero, for example when the RX stale counter fires on an idle line, the handler returns without calling geni_se_rx_dma_prep().

The next RX DMA interrupt then hits the !port->rx_dma_addr guard and returns immediately, so the RX DMA buffer is never rearmed and later input is lost.

Keep the handler on the rearm path when rx_in is zero. Warn about the unexpected zero-length DMA completion, skip received-data handling, and always call geni_se_rx_dma_prep().

Link: https://lore.kernel.org/all/20260528-serial-rx-0-byte-fix-v1-1-dc4e876c7368@oss.qualcomm.com/
Fixes: 2aaa43c ("tty: serial: qcom-geni-serial: add support for serial engine DMA")

CRs-Fixed: 4538057

[qcomlnxci]

Test jobs on 1a10ab7

• Job 115734 on lemans-evk
• Job 115733 on monaco-evk
• Job 115737 on qcs615-ride
• Job 115738 on qcs6490-rb3gen2
• Job 115735 on qcs8300-ride
• Job 115739 on qcs9100-ride-r3
• Job 115731 on x1e80100-crd

[qcomlnxci]

Test Matrix

Test Case	lemans-evk	monaco-evk	qcs615-ride	qcs6490-rb3gen2	qcs8300-ride	qcs9100-ride-r3	x1e80100-crd
BT_FW_KMD_Service	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
BT_ON_OFF	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
BT_SCAN	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
CPUFreq_Validation	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
CPU_affinity	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
DSP_AudioPD	◻️	✅ Pass	⚠️ skip	✅ Pass	✅ Pass	⚠️ skip	◻️
Ethernet	◻️	✅ Pass	⚠️ skip	⚠️ skip	⚠️ skip	⚠️ skip	◻️
Freq_Scaling	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
GIC	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
IPA	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
Interrupts	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
OpenCV	◻️	⚠️ skip	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
PCIe	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
Probe_Failure_Check	◻️	❌ Fail	✅ Pass	❌ Fail	❌ Fail	❌ Fail	◻️
RMNET	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
UFS_Validation	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
USBHost	◻️	✅ Pass	❌ Fail	❌ Fail	❌ Fail	❌ Fail	◻️
WiFi_Firmware_Driver	◻️	⚠️ skip	❌ Fail	✅ Pass	✅ Pass	✅ Pass	◻️
WiFi_OnOff	◻️	❌ Fail	⚠️ skip	✅ Pass	✅ Pass	✅ Pass	◻️
adsp_remoteproc	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	❌ Fail	◻️
cdsp_remoteproc	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	❌ Fail	◻️
gpdsp_remoteproc	◻️	✅ Pass	⚠️ skip	⚠️ skip	✅ Pass	❌ Fail	◻️
hotplug	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
irq	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
kaslr	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
pinctrl	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
qcom_hwrng	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
remoteproc	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	❌ Fail	◻️
rngtest	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
shmbridge	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
smmu	◻️	✅ Pass	❌ Fail	✅ Pass	✅ Pass	❌ Fail	◻️
watchdog	◻️	✅ Pass	✅ Pass	✅ Pass	✅ Pass	✅ Pass	◻️
wpss_remoteproc	◻️	✅ Pass	⚠️ skip	✅ Pass	✅ Pass	✅ Pass	◻️