From: sashiko-bot@kernel.org
To: "Ferry Toth" <ftoth@exalondelft.nl>
Cc: linux-serial@vger.kernel.org
Subject: Re: [PATCH v1 1/1] Revert "serial: 8250_port: Drop duplicate NULL check"
Date: Sat, 10 Oct 2026 19:49:13 +0000 [thread overview]
Message-ID: <sashiko-outbox-166854@kernel.org> (raw)
In-Reply-To: <20261010193755.187706-2-ftoth@exalondelft.nl>
> 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 <ftoth@exalondelft.nl>
Sashiko has reviewed this patch and found no issues. It looks great!
--
Sashiko AI review · https://sashiko.dev/#/patchset/20261010193755.187706-2-ftoth@exalondelft.nl?part=1
next prev parent reply other threads:[~2026-10-10 19:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-10 19:37 [PATCH v1 1/1] Revert "serial: 8250_port: Drop duplicate NULL check" Ferry Toth
2026-10-10 19:49 ` sashiko-bot [this message]
2026-10-11 5:35 ` Greg Kroah-Hartman
2026-10-11 19:28 ` Ferry Toth
2026-10-12 20:28 ` Andy Shevchenko
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