linux-kernel - Re: Regarding AHCI_MAX_SG and (ATA_HORKAGE_MAX_SEC

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Date:	Wed, 10 Aug 2016 17:19:51 +0000
From:	Tom Yan <tom.ty89@...il.com>
To:	David Milburn <dmilburn@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-block@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Regarding AHCI_MAX_SG and (ATA_HORKAGE_MAX_SEC_1024)

On 10 August 2016 at 15:41, David Milburn <dmilburn@...hat.com> wrote:
> Hi,
>
> The 168 makes AHCI_CMD_TBL_SZ equal to 2816
>
> AHCI_CMD_TBL_SZ = AHCI_CMD_TBL_HDR_SZ + (AHCI_MAX_SG * 16)
> AHCI_CMD_TBL_SZ = 128 + (168 * 16)
>
> I think if you add in AHCI_CMD_SLOT_SZ (1024) and AHCI_RX_FIS_SZ (256)
> the DMA is 4K aligned, I think that is where the 168 came from.

Looks like the right guess. Though AHCI_PORT_PRIV_DMA_SZ is not:

AHCI_CMD_SLOT_SZ (1024) + AHCI_CMD_TBL_SZ (2816) + AHCI_RX_FIS_SZ (256) = 4096

but:

AHCI_CMD_SLOT_SZ (1024) + AHCI_CMD_TBL_AR_SZ (2816 * 32 = 90112) +
AHCI_RX_FIS_SZ (256) = 91392

and AHCI_PORT_PRIV_FBS_DMA_SZ is:

AHCI_CMD_SLOT_SZ (1024) + AHCI_CMD_TBL_AR_SZ (2816 * 32 = 90112) +
AHCI_RX_FIS_SZ * 16 (4096) = 95232

>
> Thanks,
> David
>
>