linux-kernel - Re: Posted Write onto a PCI end point device using Linux

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Message-ID: <AANLkTi=V_MD5MqkPfBSD0P+J0vYgS3nwHZA37SOvYW-Z@mail.gmail.com>
Date:	Tue, 7 Dec 2010 22:55:47 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Sanka Piyaratna <cesanka@...oo.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Posted Write onto a PCI end point device using Linux

On Tue, Dec 7, 2010 at 9:57 PM, Sanka Piyaratna <cesanka@...oo.com> wrote:
> Hi Robert,
> Could you please tell me how I can initiate a posted write towards a PCIe
> endpoint with larger than 32 bit payload using Linux?
> Thanks and regards,

You can try writeq to get a 64-bit payload, but I don't think it's
available on all platforms. In particular with a 32-bit CPU, it may
not be possible at all. If you need to send bigger payloads then you
need to use DMA.

>
> Sanka Piyaratna
>
> ________________________________
> From: Robert Hancock <hancockrwd@...il.com>
> To: Sanka Piyaratna <cesanka@...oo.com>
> Cc: linux-kernel@...r.kernel.org
> Sent: Wed, 8 December, 2010 12:16:54 PM
> Subject: Re: Posted Write onto a PCI end point device using Linux
>
> On 12/07/2010 05:29 AM, Sanka Piyaratna wrote:
>> Hi,
>>
>>
>> I am wondering whether it is possible to issue a posted write using the
>> host
>> computer's root complex towards an PCI express end point. I have done this
>> using
>>
>> DMA in the past. However, if posted writes are possible that would save a
>> lot of
>>
>> time and effort and would be quicker too.
>
> Writes from the CPU to PCI memory are always posted. However, the posted
> write buffer size is usually quite limited and so this probably will
> still cause CPU overhead when writing any significant amount of data
> this way.
>
>
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