From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 0D4C1DE361 for ; Thu, 9 Oct 2008 07:45:27 +1100 (EST) Subject: Re: 8600 serial support From: Benjamin Herrenschmidt To: Kevin Diggs In-Reply-To: <48ED0F30.7080103@hypersurf.com> References: <48ED0F30.7080103@hypersurf.com> Content-Type: text/plain Date: Thu, 09 Oct 2008 07:45:11 +1100 Message-Id: <1223498711.8157.90.camel@pasglop> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org Reply-To: benh@kernel.crashing.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2008-10-08 at 12:51 -0700, Kevin Diggs wrote: > Hi, > > I thought I might take a whack at fixing the 2.6 serial driver > for my 8600. At the top of pmac_zilog.c (2.6.26) there is a todo for DMA. > A quick glance at macserial.c (2.4.31) suggests it has dbdma support for > receive. Anyone know of any pitfalls for adding dbdma support for > pmac_zilog.c? Yes, it's not totally trivial and I wouldn't recommend using the weirdo code in macserial (it does things that I don't understand how they work with the dbdma engine). The best way I see is to start from scratch with two different mechanisms: - For Tx, that's the easiest, the fire off DMA's for outgoing chars, maybe queue up a few descriptors to let data accumulate. - For Rx, one descriptor per byte. That sucks but I think that's also what Apple does. No need to have a huge Rx buffer anyway. That gives you precise Rx status to the byte. Ben.