From: Kars de Jong <jongk@linux-m68k.org>
To: Finn Thain <fthain@telegraphics.com.au>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
Michael Schmitz <schmitzmic@gmail.com>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] esp_scsi: Clear Transfer Count registers before PIO transfers
Date: Sun, 17 Nov 2019 07:26:16 +0100 [thread overview]
Message-ID: <CACz-3rjHAyi6kMQ6j9YALLm1ApYrsqKiTnGNPUhxqqEuRJ9TjQ@mail.gmail.com> (raw)
In-Reply-To: <2bbb6359d542f5882be67c415ecc25ad2d9eeb5e.1573875417.git.fthain@telegraphics.com.au>
Hi Finn,
Op za 16 nov. 2019 om 04:36 schreef Finn Thain <fthain@telegraphics.com.au>:
>
> The zorro_esp driver uses both PIO and DMA transfers. If a failed DMA
> transfer happened to be followed by a PIO transfer, the TCLOW and TCMED
> registers would not get cleared. It is theoretically possible that the
> stale value from the transfer counter or the TCLOW/TCMED registers
> could then be used by the controller and the driver. Avoid that by
> clearing these registers before each PIO transfer.
Are you sure this is really needed?
The only place where the driver reads these registers is after a data
transfer. These are done using DMA on all Zorro boards, so I don’t
think there’s a risk of stale values from a PIO transfer there.
The only place the controller reads these registers is when a DMA
command is issued. The only place where that is done is in the
zorro_esp send_dma_command() functions. These all set both registers
explicitly before issuing the DMA command to the controller, so I
don’t think there’s a risk there either.
Kind regards,
Kars.
next prev parent reply other threads:[~2019-11-17 6:26 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-16 3:36 [PATCH] esp_scsi: Clear Transfer Count registers before PIO transfers Finn Thain
2019-11-16 4:30 ` Michael Schmitz
2019-11-16 23:02 ` Finn Thain
2019-11-17 6:26 ` Kars de Jong [this message]
2019-11-17 6:29 ` Kars de Jong
2019-11-17 23:13 ` Finn Thain
2019-11-17 23:26 ` Finn Thain
2019-11-18 8:13 ` Kars de Jong
2019-11-18 23:04 ` Finn Thain
2019-11-19 23:12 ` Finn Thain
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