linux-kernel - Re: Regarding AHCI_MAX_SG and (ATA_HORKAGE_MAX_SEC

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Date:	Wed, 10 Aug 2016 14:38:08 -0500
From:	David Milburn <dmilburn@...hat.com>
To:	Tom Yan <tom.ty89@...il.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 08/10/2016 12:19 PM, Tom Yan wrote:
> 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
>

Yes, but in both cases mem_dma gets adjusted for AHCI_CMD_SLOT_SZ (1024)
and rx_fis_sz (256 or 4096 in fbs case).

Thanks,
David