rfid: lower MFRC522 SPI clock to 2 MHz for clone-reader self-test stability

main/rfid_manager.c

@@ -22,8 +22,9 @@ static const char *TAG = "rfid";
 #define RC522_TASK_PRIORITY    (4)
 
 /* Conservative clock for MFRC522 clones. If the FIFO self-test still
- * reports a mismatch at boot, lower this (e.g. 2000000) or check power. */
-#define RC522_SPI_CLK_HZ (4000000)
+ * reports a mismatch at boot, lower this further (e.g. 1000000) or check
+ * power/wiring. Many clone readers glitch at 4MHz on a shared bus. */
+#define RC522_SPI_CLK_HZ (2000000)
 #define RC522_START_ATTEMPTS (3)
 
 static rc522_driver_handle_t s_driver;