From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3177EC43331 for ; Sat, 9 Nov 2019 22:53:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0069820B7C for ; Sat, 9 Nov 2019 22:53:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726467AbfKIWxg (ORCPT ); Sat, 9 Nov 2019 17:53:36 -0500 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:37406 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726448AbfKIWxg (ORCPT ); Sat, 9 Nov 2019 17:53:36 -0500 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id EC6942A4DD; Sat, 9 Nov 2019 17:53:31 -0500 (EST) Date: Sun, 10 Nov 2019 09:53:33 +1100 (AEDT) From: Finn Thain To: Kars de Jong cc: "James E.J. Bottomley" , "Martin K. Petersen" , linux-scsi@vger.kernel.org, linux-m68k@vger.kernel.org Subject: Re: [PATCH] zorro_esp: increase maximum dma length to 65536 bytes In-Reply-To: <20191109191400.8999-1-jongk@linux-m68k.org> Message-ID: References: <20191109191400.8999-1-jongk@linux-m68k.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-m68k-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-m68k@vger.kernel.org On Sat, 9 Nov 2019, Kars de Jong wrote: > When using this driver on a Blizzard 1260, there were failures whenever > DMA transfers from the SCSI bus to memory of 65535 bytes were followed by a > DMA transfer of 1 byte. This caused the byte at offset 65535 to be > overwritten with 0xff. The Blizzard hardware can't handle single byte DMA > transfers. > > Besides this issue, limiting the DMA length to something that is not a > multiple of the page size is very inefficient on most file systems. > Makes sense. You may want to add, Fixes: b7ded0e8b0d1 ("scsi: zorro_esp: Limit DMA transfers to 65535 bytes") > It seems this limit was chosen because the DMA transfer counter of the ESP > by default is 16 bits wide, thus limiting the length to 65535 bytes. > However, the value 0 means 65536 bytes, which is handled by the ESP and the > Blizzard just fine. It is also the default maximum used by esp_scsi when > drivers don't provide their own dma_length_limit() function. > > Signed-off-by: Kars de Jong > --- > drivers/scsi/zorro_esp.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/scsi/zorro_esp.c b/drivers/scsi/zorro_esp.c > index ca8e3abeb2c7..4448567c495d 100644 > --- a/drivers/scsi/zorro_esp.c > +++ b/drivers/scsi/zorro_esp.c > @@ -218,7 +218,7 @@ static int fastlane_esp_irq_pending(struct esp *esp) > static u32 zorro_esp_dma_length_limit(struct esp *esp, u32 dma_addr, > u32 dma_len) > { > - return dma_len > 0xFFFF ? 0xFFFF : dma_len; > + return dma_len > (1U << 16) ? (1U << 16) : dma_len; > } > Would it be safer to simply remove this code and leave esp_driver_ops.dma_length_limit == NULL for all board types? -- > static void zorro_esp_reset_dma(struct esp *esp) >