From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: SIL24: pcie_set_readrq 4096
Date: Thu, 22 Jul 2010 15:18:37 +0200
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To: Jassi Brar <jassisinghbrar@gmail.com>
Cc: linux-pci@vger.kernel.org, linux-ide@vger.kernel.org, jgarzik@pobox.com

Hello,

On 07/22/2010 04:47 AM, Jassi Brar wrote:
>   After implementing driver for PCIe RC controller of a SOC, I came
> across peculiarity
> while testing SIL3132 directly connected to the root port.
> 
> My RC IP is configured for maximum of 256bytes of payload size.
> The sata_sil24 driver unconditionally sets pcie_set_readrq(pdev, 4096)
> for the endpoint
> which apparently works for 'every' other host irrespective of their capacity.
> 
> In my case it works only if I change to
>   pcie_set_readrq(pdev, 256)
> 
> Shouldn't the Linux PCI have provision to allow max_read/payload_size
> not higher than
> the least of max capacities of all agents in the chain ?
> 
> I see similar use of pcie_set_readrq(pdev, 4096), so could be I am
> missing something ?

It's been a while since I read pci-e spec but IIUC readrq size and
payload size are independent and if readrq is larger than payload size
it's supposed to complete in multiple steps.  I could be wrong tho.

Thanks.

-- 
tejun