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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3912bfe0004sm13025061f8f.40.2025.03.09.18.29.04 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 09 Mar 2025 18:29:04 -0700 (PDT) From: =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= To: qemu-devel@nongnu.org Cc: Peter Maydell , =?utf-8?q?Marc-Andr=C3=A9_Lure?= =?utf-8?q?au?= , =?utf-8?q?Alex_Benn=C3=A9e?= , Mark Cave-Ayland , qemu-arm@nongnu.org, Paolo Bonzini , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Mikko Rapeli Subject: [PATCH v7 7/7] hw/char/pl011: Implement TX FIFO Date: Mon, 10 Mar 2025 02:28:25 +0100 Message-ID: <20250310012825.79614-8-philmd@linaro.org> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250310012825.79614-1-philmd@linaro.org> References: <20250310012825.79614-1-philmd@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::432; envelope-from=philmd@linaro.org; helo=mail-wr1-x432.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org If the UART back-end chardev doesn't drain data as fast as stdout does or blocks, buffer in the TX FIFO to try again later. This avoids having the IO-thread busy waiting on chardev back-ends, reported recently when testing the Trusted Reference Stack and using the socket backend. Implement registering a front-end 'watch' callback on back-end events, so we can resume transmitting when the back-end is writable again, not blocking the main loop. Similarly to the RX FIFO path, FIFO level selection is not implemented (interrupt is triggered when a single byte is available in the FIFO). Reported-by: Mikko Rapeli Suggested-by: Alex Bennée Reviewed-by: Peter Maydell Signed-off-by: Philippe Mathieu-Daudé --- hw/char/pl011.c | 35 +++++++++++++++++++++++++++-------- hw/char/trace-events | 1 + 2 files changed, 28 insertions(+), 8 deletions(-) diff --git a/hw/char/pl011.c b/hw/char/pl011.c index 6d26a3e13f8..d93cd8b3f0e 100644 --- a/hw/char/pl011.c +++ b/hw/char/pl011.c @@ -258,6 +258,10 @@ static gboolean pl011_xmit_cb(void *do_not_use, GIOCondition cond, void *opaque) count = fifo8_num_used(&s->xmit_fifo); trace_pl011_fifo_tx_xmit_used(count); + if (count < 1) { + /* FIFO empty */ + return G_SOURCE_REMOVE; + } if (!qemu_chr_fe_backend_connected(&s->chr)) { /* Instant drain the fifo when there's no back-end. */ @@ -265,15 +269,23 @@ static gboolean pl011_xmit_cb(void *do_not_use, GIOCondition cond, void *opaque) return G_SOURCE_REMOVE; } - buf[0] = fifo8_pop(&s->xmit_fifo); - bytes_consumed = 1; + count = fifo8_peek_buf(&s->xmit_fifo, buf, fifo8_num_used(&s->xmit_fifo)); + trace_pl011_fifo_tx_xmit_peek(count); - /* - * XXX this blocks entire thread. Rewrite to use - * qemu_chr_fe_write and background I/O callbacks - */ - qemu_chr_fe_write_all(&s->chr, buf, bytes_consumed); + /* Transmit as much data as we can. */ + bytes_consumed = qemu_chr_fe_write(&s->chr, buf, count); trace_pl011_fifo_tx_xmit_consumed(bytes_consumed); + if (bytes_consumed < 0) { + /* Error in back-end: drain the fifo. */ + pl011_drain_tx(s); + return G_SOURCE_REMOVE; + } else if (bytes_consumed == 0) { + /* Couldn't send anything, try again later */ + return G_SOURCE_CONTINUE; + } + + /* Pop the data we could transmit. */ + fifo8_drop(&s->xmit_fifo, bytes_consumed); s->int_level |= INT_TX; s->flags &= ~PL011_FLAG_TXFF; @@ -284,6 +296,11 @@ static gboolean pl011_xmit_cb(void *do_not_use, GIOCondition cond, void *opaque) pl011_update(s); + if (!emptied_fifo) { + /* Reschedule another transmission if we couldn't transmit all. */ + return G_SOURCE_CONTINUE; + } + return G_SOURCE_REMOVE; } @@ -313,7 +330,9 @@ static void pl011_write_txdata(PL011State *s, uint8_t data) trace_pl011_fifo_tx_put(data); pl011_loopback_tx(s, data); fifo8_push(&s->xmit_fifo, data); - s->flags |= PL011_FLAG_TXFF; + if (pl011_is_tx_fifo_full(s)) { + s->flags |= PL011_FLAG_TXFF; + } s->flags &= ~PL011_FLAG_TXFE; pl011_xmit(s); diff --git a/hw/char/trace-events b/hw/char/trace-events index 730d6292a2d..c377f971a6c 100644 --- a/hw/char/trace-events +++ b/hw/char/trace-events @@ -68,6 +68,7 @@ pl011_fifo_rx_put(uint32_t c, unsigned read_count, size_t rx_fifo_depth) "RX FIF pl011_fifo_rx_full(void) "RX FIFO now full, RXFF set" pl011_fifo_tx_is_full(const char *desc, bool full) "mode:%s full:%u" pl011_fifo_tx_put(uint8_t byte) "TX FIFO push char [0x%02x]" +pl011_fifo_tx_xmit_peek(unsigned sent) "TX FIFO peek %u chars" pl011_fifo_tx_xmit_used(unsigned sent) "TX FIFO used %u chars" pl011_fifo_tx_xmit_consumed(unsigned sent) "TX FIFO consumed %u chars" pl011_fifo_tx_overrun(void) "TX FIFO overrun"