linux-kernel - Re: HELP: Is writeq an atomic operation??

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Date:	Fri, 02 May 2008 16:04:00 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	"Moore\, Eric" <Eric.Moore@....com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: HELP:  Is writeq an atomic operation??

 > Here is a trace from pci express analyzer.   I'm sending
 > 0x0800010000000000 to the adress DD1400C0 using writeq.   Notice that in
 > the TLP header it sent a 32bit Memory write with data length of two.

By the way, are you worried that there is something wrong with this
trace?  Your write went out in a single PCIe packet, so it looks perfect
to me.  Does the "Mem MWr(32)" worry you?  I can't see why it would be a
problem -- the PCIe TLP only has one type of memory write transaction
(well, except for 32-bit or 64-bit addressing, but you don't care about
that), and memory write transactions are sent as a string of 32-bit
chunks, so there's no other way a 64-bit write could be sent.

 > Trace follows:
 > 
 > Link Tra(597) Downstream 2.5(x1) TLP(1992) Mem MWr(32)(10:00000) TC(0)
 > TD(0) 
 > _______| EP(0) Attributes(01) Length(2) RequesterID(000:02:0) Tag(8) 
 > _______| Address(DD1400C0) 1st BE(1111) Last BE(1111) Data(08000100
 > 00000000) 
 > _______| VC ID(0) Explicit ACK(Packet #1195) Metrics # Packets(2) 
 > _______| Time Stamp(0003 . 120 181 840 s) 
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