diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig index d1b27b0522a3..9a721f98eedc 100644 --- a/drivers/tty/hvc/Kconfig +++ b/drivers/tty/hvc/Kconfig @@ -86,6 +86,27 @@ config HVC_DCC driver. This console is used through a JTAG only on ARM. If you don't have a JTAG then you probably don't want this option. +config HVC_DCC_SERIALIZE_SMP + bool "Use DCC only on core 0" + depends on SMP && HVC_DCC + help + Some debuggers, such as Trace32 from Lauterbach GmbH, do not handle + reads/writes from/to DCC on more than one core. Each core has its + own DCC device registers, so when a core reads or writes from/to DCC, + it only accesses its own DCC device. Since kernel code can run on + any core, every time the kernel wants to write to the console, it + might write to a different DCC. + + In SMP mode, Trace32 only uses the DCC on core 0. In AMP mode, it + creates multiple windows, and each window shows the DCC output + only from that core's DCC. The result is that console output is + either lost or scattered across windows. + + Selecting this option will enable code that serializes all console + input and output to core 0. The DCC driver will create input and + output FIFOs that all cores will use. Reads and writes from/to DCC + are handled by a workqueue that runs only core 0. + config HVC_RISCV_SBI bool "RISC-V SBI console support" depends on RISCV_SBI_V01 diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c index 8e0edb7d93fd..e1ebcdd5fe8d 100644 --- a/drivers/tty/hvc/hvc_dcc.c +++ b/drivers/tty/hvc/hvc_dcc.c @@ -3,8 +3,10 @@ #include #include +#include #include #include +#include #include #include @@ -67,26 +69,177 @@ static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count) return i; } +/* + * Check if the DCC is enabled. If CONFIG_HVC_DCC_SERIALIZE_SMP is enabled, + * then we assume then this function will be called first on core 0. That + * way, dcc_core0_available will be true only if it's available on core 0. + */ static bool hvc_dcc_check(void) { unsigned long time = jiffies + (HZ / 10); +#ifdef CONFIG_HVC_DCC_SERIALIZE_SMP + static bool dcc_core0_available; + + /* + * If we're not on core 0, but we previously confirmed that DCC is + * active, then just return true. + */ + if (smp_processor_id() && dcc_core0_available) + return true; +#endif + /* Write a test character to check if it is handled */ __dcc_putchar('\n'); while (time_is_after_jiffies(time)) { - if (!(__dcc_getstatus() & DCC_STATUS_TX)) + if (!(__dcc_getstatus() & DCC_STATUS_TX)) { +#ifdef CONFIG_HVC_DCC_SERIALIZE_SMP + dcc_core0_available = true; +#endif return true; + } } return false; } +#ifdef CONFIG_HVC_DCC_SERIALIZE_SMP + +static void dcc_put_work_fn(struct work_struct *work); +static void dcc_get_work_fn(struct work_struct *work); +static DECLARE_WORK(dcc_pwork, dcc_put_work_fn); +static DECLARE_WORK(dcc_gwork, dcc_get_work_fn); +static DEFINE_SPINLOCK(dcc_lock); +static DEFINE_KFIFO(inbuf, unsigned char, 128); +static DEFINE_KFIFO(outbuf, unsigned char, 1024); + +/* + * Workqueue function that writes the output FIFO to the DCC on core 0. + */ +static void dcc_put_work_fn(struct work_struct *work) +{ + unsigned char ch; + + spin_lock(&dcc_lock); + + /* While there's data in the output FIFO, write it to the DCC */ + while (kfifo_get(&outbuf, &ch)) + hvc_dcc_put_chars(0, &ch, 1); + + /* While we're at it, check for any input characters */ + while (!kfifo_is_full(&inbuf)) { + if (!hvc_dcc_get_chars(0, &ch, 1)) + break; + kfifo_put(&inbuf, ch); + } + + spin_unlock(&dcc_lock); +} + +/* + * Workqueue function that reads characters from DCC and puts them into the + * input FIFO. + */ +static void dcc_get_work_fn(struct work_struct *work) +{ + unsigned char ch; + + /* + * Read characters from DCC and put them into the input FIFO, as + * long as there is room and we have characters to read. + */ + spin_lock(&dcc_lock); + + while (!kfifo_is_full(&inbuf)) { + if (!hvc_dcc_get_chars(0, &ch, 1)) + break; + kfifo_put(&inbuf, ch); + } + spin_unlock(&dcc_lock); +} + +/* + * Write characters directly to the DCC if we're on core 0 and the FIFO + * is empty, or write them to the FIFO if we're not. + */ +static int hvc_dcc0_put_chars(uint32_t vt, const char *buf, + int count) +{ + int len; + + spin_lock(&dcc_lock); + if (smp_processor_id() || (!kfifo_is_empty(&outbuf))) { + len = kfifo_in(&outbuf, buf, count); + spin_unlock(&dcc_lock); + /* + * We just push data to the output FIFO, so schedule the + * workqueue that will actually write that data to DCC. + */ + schedule_work_on(0, &dcc_pwork); + return len; + } + + /* + * If we're already on core 0, and the FIFO is empty, then just + * write the data to DCC. + */ + len = hvc_dcc_put_chars(vt, buf, count); + spin_unlock(&dcc_lock); + + return len; +} + +/* + * Read characters directly from the DCC if we're on core 0 and the FIFO + * is empty, or read them from the FIFO if we're not. + */ +static int hvc_dcc0_get_chars(uint32_t vt, char *buf, int count) +{ + int len; + + spin_lock(&dcc_lock); + + if (smp_processor_id() || (!kfifo_is_empty(&inbuf))) { + len = kfifo_out(&inbuf, buf, count); + spin_unlock(&dcc_lock); + + /* + * If the FIFO was empty, there may be characters in the DCC + * that we haven't read yet. Schedule a workqueue to fill + * the input FIFO, so that the next time this function is + * called, we'll have data. + */ + if (!len) + schedule_work_on(0, &dcc_gwork); + + return len; + } + + /* + * If we're already on core 0, and the FIFO is empty, then just + * read the data from DCC. + */ + len = hvc_dcc_get_chars(vt, buf, count); + spin_unlock(&dcc_lock); + + return len; +} + +static const struct hv_ops hvc_dcc_get_put_ops = { + .get_chars = hvc_dcc0_get_chars, + .put_chars = hvc_dcc0_put_chars, +}; + +#else + static const struct hv_ops hvc_dcc_get_put_ops = { .get_chars = hvc_dcc_get_chars, .put_chars = hvc_dcc_put_chars, }; +#endif + static int __init hvc_dcc_console_init(void) { int ret;