Linux-SCSI Archive on
 help / color / Atom feed
From: Michael Schmitz <>
To: Kars de Jong <>
Cc: James Bottomley <>,
	"Martin K. Petersen" <>,,
Subject: Re: [PATCH] zorro_esp: increase maximum dma length to 65536 bytes
Date: Mon, 11 Nov 2019 08:26:32 +1300
Message-ID: <> (raw)
In-Reply-To: <>

Hi Kars,

thanks for your patch!

On 10/11/19 10:01 PM, Kars de Jong wrote:
> Hi Michael,
> Op zo 10 nov. 2019 om 03:36 schreef Michael Schmitz <>:
>> All of the old board-specific drivers used a max transfer length of
>> 0x1000000, only the fastlane driver used 0xfffc.
> Yes, I also found this when checking the old drivers.
>> That lower limit might
>> be due to a DMA limitation on the fastlane board. We could accommodate
>> the different limit for this board by using a board-specific
>> dma_length_limit() callback...
> Yes, I think that's the best idea for now. Oktagon also used to have a
> different limit but that was never ported to the new ESP core.

I can't remember the details, but as far as I recall it, the Oktagon 
used pseudo-DMA rather than hardware DMA. At the time I started porting 
Zorro ESP drivers to the new core, pseudo-DMA code was available for Mac 
only, and no PIO transfer for data phases at all, so I decided to leave 
that out altogether.

Might be a lot easier now that Finn has moved the PIO support code into 
the core driver. Someone could start with a PIO mode driver and add PDMA 

>>> case for any of the cards the zorro_esp drives, it might be better to
>>> lower the max length to 61440 (64k-4k) so the residual is a page.
>> For the benefit of keeping the code simple, and avoid retesting the
>> fastlane board, that might indeed be the better solution.
> But it's slower... :-P
I wonder what max. transfer size had been used so far, in the majority 
of cases. I hadn't observed this bug in my tests of the ESP driver on 
elgar. So it might not matter so much in practice.
> Also, I may be adding another board-specific version for the Blizzard
> 12x0 IV to enable 24-bit transfers, like the am53c974 driver does, in
> a later patch.

If we can differentiate between the Mark IV board and the Mark II board 
in a reliable way, fine. I can't remember whether I've had a report on 
that ever.

I'd suggest to change the transfer size limit to 60k in the first 
instance, and add board-specific tweaks as needed when you add 24 bit 
DMA support for the Mark IV.



> Kind regards,
> Kars.

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2019-11-09 19:14 ` Kars de Jong
2019-11-09 20:12   ` James Bottomley
2019-11-10  2:36     ` Michael Schmitz
2019-11-10  9:01       ` Kars de Jong
2019-11-10 19:26         ` Michael Schmitz [this message]
2019-11-11  8:47           ` Kars de Jong
2019-11-10 19:35       ` James Bottomley
2019-11-12 17:55         ` [PATCH v2] zorro_esp: Limit DMA transfers to 65536 bytes (except on Fastlane) Kars de Jong
2019-11-12 22:46           ` Finn Thain
2019-11-13  2:27           ` Martin K. Petersen
2019-11-12  9:34       ` [PATCH] zorro_esp: increase maximum dma length to 65536 bytes Kars de Jong
2019-11-09 22:53   ` Finn Thain
2019-11-10  9:06     ` Kars de Jong

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-SCSI Archive on

Archives are clonable:
	git clone --mirror linux-scsi/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-scsi linux-scsi/ \
	public-inbox-index linux-scsi

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone