From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3EAA249AA49; Mon, 12 Oct 2026 20:28:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791836892; cv=none; b=r3Fu4NcMjWmq5t/N0DlqCjqvV2hyy9mewBNZR17Vxb+fW8i+3mhb0buolNK+g4gQgnvXTZIhebZCmgZFQe+hE7DlTlgvILfszd5IRYhBwWNZfLFPGbTlOSj98OIC69Vy3698KIF9xPNIUB3Cxbzvvj03sQwTNj0hxAESrkVUx5g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791836892; c=relaxed/simple; bh=HhcV9cAX46l21QPoJJnWGRnUgvHnzefXF/e5LbBtemk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Tsd2K73fXfK0p+tiFkXiTLRQjzVs0Y+8FwHvvlCymgcK8KgrgSh0sj9M+aJUWxR2d+HqWMP8WKpssoqLSIdpRJH4BTbtSVwsDcO0VEK4RaHLdurPU2toGKtC7KQRPIMAdARbI6yIPAcWpXshMxEaiBS0cgb2LegztrX35uGRJv8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=pass smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=FeoRhPci; arc=none smtp.client-ip=192.198.163.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="FeoRhPci" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1791836888; x=1823372888; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=HhcV9cAX46l21QPoJJnWGRnUgvHnzefXF/e5LbBtemk=; b=FeoRhPciwJZIruQCljBI5hk8Cfhzy49zJmbCnrJ25EPmM9oqvmADDBUg lW9yO0MaP6Lhg5xoytl6KBLAXLIVdUk8HorwU59Bh1znBQFeBVpJ9teGf NtxZHdrPj8ZnquIOUyEq2S/UvJt3qQVLCYoyksefS0wuQvBXZ4XrWn88Q RiE9DXuz+Kv1dcFxCU79xIP3sZYB8RV4758dRd5cIDk2ZXU0w7zLgM+SW Si4YA7w7IWZcZYN70JdqhwzHU8jVbtSTiGRfNtZw+Pgn290TOtahr7/Y2 a7AX9IPB7hArdPGwe7oboVvN4ecGKzSbeJKtfzjWgbA0iW6Tj+Fg9Inj9 Q==; X-CSE-ConnectionGUID: VUALo0awRsOakQBss/gaHA== X-CSE-MsgGUID: bg5sPVHsQ2eiSQAqP8zj0A== X-IronPort-AV: E=McAfee;i="6800,10657,11933"; a="560464" X-IronPort-AV: E=Sophos;i="6.27,154,1787036400"; d="scan'208";a="560464" Received: from orviesa008.jf.intel.com ([10.64.159.148]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Oct 2026 13:28:07 -0700 X-CSE-ConnectionGUID: yQb4YRTvQTWRrY+FLY4hpQ== X-CSE-MsgGUID: bRPGHh87Si2dv5uN3kaxdQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,154,1787036400"; d="scan'208";a="904251" Received: from pgcooper-mobl3.ger.corp.intel.com (HELO localhost) ([10.245.244.179]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Oct 2026 13:28:05 -0700 Date: Mon, 12 Oct 2026 23:28:02 +0300 From: Andy Shevchenko To: Ferry Toth Cc: Greg Kroah-Hartman , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , John Ogness , Crescent Hsieh , Hugo Villeneuve , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Jiri Slaby , stable@vger.kernel.org Subject: Re: [PATCH v1 1/1] Revert "serial: 8250_port: Drop duplicate NULL check" Message-ID: References: <20261010193755.187706-2-ftoth@exalondelft.nl> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261010193755.187706-2-ftoth@exalondelft.nl> Organization: Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs, Bertel Jungin Aukio 5, 02600 Espoo 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. As discussed off-list with Ferry the culprit patch was inspired by 8250_omap implementation which may have the same bug lurking. Thanks, Ferry, for a good catch! Acked-by: Andy Shevchenko -- With Best Regards, Andy Shevchenko