Re: [PATCH] zorro_esp: increase maximum dma length to 65536 bytes

From: Kars de Jong <jongk@linux-m68k.org>
To: Michael Schmitz <schmitzmic@gmail.com>
Cc: James Bottomley <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org, linux-m68k@vger.kernel.org
Subject: Re: [PATCH] zorro_esp: increase maximum dma length to 65536 bytes
Date: Sun, 10 Nov 2019 10:01:58 +0100	[thread overview]
Message-ID: <CACz-3rjUh8tcShX5OPi+37JvF8PqG-8AEf5uMQHjMynSaVa1gw@mail.gmail.com> (raw)
In-Reply-To: <6b914b12-cbc7-6fe6-7cba-3e89b2f6f19b@gmail.com>

Hi Michael,

Op zo 10 nov. 2019 om 03:36 schreef Michael Schmitz <schmitzmic@gmail.com>:
> 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.

> > 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

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.

Kind regards,

Kars.