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From: James Bottomley <jejb@linux.ibm.com>
To: Michael Schmitz <schmitzmic@gmail.com>,
	Kars de Jong <jongk@linux-m68k.org>,
	"Martin K. Petersen" <martin.petersen@oracle.com>
Cc: 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 11:35:13 -0800
Message-ID: <1573414513.3230.4.camel@linux.ibm.com> (raw)
In-Reply-To: <6b914b12-cbc7-6fe6-7cba-3e89b2f6f19b@gmail.com>

On Sun, 2019-11-10 at 15:36 +1300, Michael Schmitz wrote:
> All of the old board-specific drivers used a max transfer length of 
> 0x1000000, only the fastlane driver used 0xfffc. 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...

Sure, that implies the minimum dma burst length is 4 bytes ...

> > 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.

... which means you don't have to lower the limit by 4k as I suggested,
 because I was being incredibly conservative about what the dma burst
length might be, just use 0xfffc as the default.  I think raising to
0x1000000 for boards which can support it is fine too if you want to
add the extra logic to the driver.

James


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CACz-3rh9ZCyU1825yU8xxty5BGrwFhpbjKNoWnn0mGiv_h2Kag@mail.gmail.com>
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
2019-11-11  8:47           ` Kars de Jong
2019-11-10 19:35       ` James Bottomley [this message]
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

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