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[2a02:a466:68ed:1:6152:f99d:3762:f020]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c31a9ac9ecfsm399541866b.74.2026.10.11.12.28.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 11 Oct 2026 12:28:46 -0700 (PDT) Message-ID: <2fe443ce-2d3e-4a1d-aaf0-0aef68da4cf0@gmail.com> Date: Sun, 11 Oct 2026 21:28:41 +0200 Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/1] Revert "serial: 8250_port: Drop duplicate NULL check" To: Greg Kroah-Hartman Cc: =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= , John Ogness , Andy Shevchenko , Crescent Hsieh , Hugo Villeneuve , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Jiri Slaby , stable@vger.kernel.org References: <20261010193755.187706-2-ftoth@exalondelft.nl> <2026101151-regroup-caterer-b92d@gregkh> Content-Language: en-US From: Ferry Toth In-Reply-To: <2026101151-regroup-caterer-b92d@gregkh> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Op 11-10-2026 om 07:35 schreef Greg Kroah-Hartman: > On Sat, Oct 10, 2026 at 09:37:56PM +0200, Ferry Toth wrote: >> 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. > Ugh, sorry about missing that. I'll queue this up when I get a chance > in the next few days, thanks for posting it. > > greg k-h No worries, sorry I found it this late. I have been behind testing kernels and only now trying to catch up. Ferry