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Date:      Sun, 30 Dec 2012 11:23:11 -0700
From:      Scott Long <scott4long@yahoo.com>
To:        Ian Lepore <freebsd@damnhippie.dyndns.org>
Cc:        powerpc@freebsd.org, marcel@freebsd.org, mips@freebsd.org, John Baldwin <jhb@freebsd.org>, "mav@freebsd.org Motin" <mav@freebsd.org>, "attilio@FreeBSD.org Rao" <attilio@freebsd.org>, Jeff Roberson <jroberson@jroberson.net>, sparc64@freebsd.org, arm@freebsd.org, kib@freebsd.org
Subject:   Re: Call for testing and review, busdma changes
Message-ID:  <30DCC8A9-8E26-4500-AF33-2D81981B554F@yahoo.com>
In-Reply-To: <1356891693.54953.31.camel@revolution.hippie.lan>
References:  <alpine.BSF.2.00.1212080841370.4081@desktop> <1355077061.87661.320.camel@revolution.hippie.lan> <alpine.BSF.2.00.1212090840080.4081@desktop> <1355085250.87661.345.camel@revolution.hippie.lan> <alpine.BSF.2.00.1212231418120.2005@desktop> <1356381775.1129.181.camel@revolution.hippie.lan> <alpine.BSF.2.00.1212241104040.2005@desktop> <1356390225.1129.217.camel@revolution.hippie.lan> <2D98F70D-4031-4860-BABB-1F4663896234@yahoo.com> <1356891693.54953.31.camel@revolution.hippie.lan>

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On Dec 30, 2012, at 11:21 AM, Ian Lepore <freebsd@damnhippie.dyndns.org> =
wrote:

> On Mon, 2012-12-24 at 22:13 -0500, Scott Long wrote:
>>>>>=20
>>>>> Still unresolved is what to do about the remaining cases -- =
attempts to
>>>>> do dma in arbitrary buffers not obtained from bus_dmamem_alloc() =
which
>>>>> are not aligned and padded appropriately.  There was some =
discussion a
>>>>> while back, but no clear resolution.  I decided not to get bogged =
down
>>>>> by that fact and to fix the mbuf and allocated-buffer situations =
that we
>>>>> know how to deal with for now.
>>>>=20
>>=20
>> Why would these allocations not be handled as normal dynamic buffers
>> would with bus_dmamap_load()?
>>=20
>> Scott
>=20
> That's my point -- for "normal dynamic buffers" (that is, they weren't
> obtained from bus_dmamem_alloc() and they aren't mbufs) which can have
> arbitrary alignment and padding in relation to cache line boundaries =
--
> we don't handle them correctly now unless they're accidentally already
> aligned and sized to the right boundaries.  What's unresolved is how =
to
> handle them correctly if they're not aligned/padded, that is, what to =
do
> about them that avoids needing a partial cacheline flush at sync time.
>=20

Alignment is already handled.

Scott




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