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b=IF2j1HVpN7j1CkWMht9PXXhLVEFbz4mbmHep87ConlZhlEjuEOWWCwImwAtf87yKVpCTIBtHpY 2GTSBCZMqsphyst7ddEjP8An9m3cINJvVejZYaRU5hyGpYVlpiIQJx1UFR04D50fpUm+iPYPil Z6F2dY8V81TCIj3pG4ox2+0c973SQ8cLuGmdv50+A1wjUdUbqF4rhWuob+GnY2B56zbnMYGViC DoVW5kAPG+ir9oqa86B6u+WwzNfVvGSQlJo+hp/0DdDGWrlMIkoYukyFgdL0KYVu9aWwEU05TV 3lhTjCIueLOGy6eo+flqPrigXzcImWnv4T8tlxwI+Ga+7A==; Authentication-Results: webhostingserver.nl; iprev=pass (2a02-a466-68ed-1-4b1e-abe0-4124-3c9d.fixed6.kpn.net) smtp.remote-ip=2a02:a466:68ed:1:4b1e:abe0:4124:3c9d; auth=pass (PLAIN) smtp.auth=ferry.toth@elsinga.info; spf=softfail smtp.mailfrom=exalondelft.nl; dmarc=skipped header.from=exalondelft.nl; arc=none Received: from 2a02-a466-68ed-1-4b1e-abe0-4124-3c9d.fixed6.kpn.net ([2a02:a466:68ed:1:4b1e:abe0:4124:3c9d] helo=submission) by s198.webhostingserver.nl with esmtpa (Exim 4.100.1) (envelope-from ) id 1xFcuY-0000000FlNz-3TS3; Sat, 10 Oct 2026 21:39:14 +0200 From: Ferry Toth To: Greg Kroah-Hartman , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= , John Ogness , Andy Shevchenko , Crescent Hsieh , Hugo Villeneuve , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Cc: Jiri Slaby , Ferry Toth , stable@vger.kernel.org Subject: [PATCH v1 1/1] Revert "serial: 8250_port: Drop duplicate NULL check" Date: Sat, 10 Oct 2026 21:37:56 +0200 Message-ID: <20261010193755.187706-2-ftoth@exalondelft.nl> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Antivirus-Scanner: Clean mail though you should still use an Antivirus This reverts commit 7885af04df6e4efd72910200c1bfc079d61202e4. Commit 7885af04df6e ("serial: 8250_port: Drop duplicate NULL check") added `up->dma = NULL;` to serial8250_release_dma(), with the stated intent of making sure DMA would not be used again after release. However, up->dma is assigned once at probe time. serial8250_do_startup() only calls serial8250_request_dma() when up->dma is non-NULL, so after the first close the pointer stays NULL and DMA is never re-acquired. On Intel Tangier (Edison) with HSU DMA this causes a regression: the first port open uses TX DMA, the second and later opens transmit in PIO mode, producing 64-byte FIFO bursts with ~50us gaps between them. Fixes: 7885af04df6e ("serial: 8250_port: Drop duplicate NULL check") Cc: stable@vger.kernel.org Signed-off-by: Ferry Toth --- drivers/tty/serial/8250/8250_port.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 38fa45e74a37..19d0663ee756 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2428,8 +2428,8 @@ void serial8250_do_shutdown(struct uart_port *port) synchronize_irq(port->irq); - serial8250_release_dma(up); - up->dma = NULL; + if (up->dma) + serial8250_release_dma(up); scoped_guard(uart_port_lock_irqsave, port) { if (port->flags & UPF_FOURPORT) { -- 2.53.0