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, URIBL_BLOCKED autolearn=ham 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 9C529C17448 for ; Tue, 12 Nov 2019 22:46:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7D86921783 for ; Tue, 12 Nov 2019 22:46:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727249AbfKLWqL (ORCPT ); Tue, 12 Nov 2019 17:46:11 -0500 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:59654 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726932AbfKLWqK (ORCPT ); Tue, 12 Nov 2019 17:46:10 -0500 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id 4C4712A6B4; Tue, 12 Nov 2019 17:46:07 -0500 (EST) Date: Wed, 13 Nov 2019 09:46:10 +1100 (AEDT) From: Finn Thain To: Kars de Jong cc: "James E.J. Bottomley" , linux-scsi@vger.kernel.org, linux-m68k@vger.kernel.org, "Martin K. Petersen" , schmitzmic@gmail.com Subject: Re: [PATCH v2] zorro_esp: Limit DMA transfers to 65536 bytes (except on Fastlane) In-Reply-To: <20191112175523.23145-1-jongk@linux-m68k.org> Message-ID: References: <1573414513.3230.4.camel@linux.ibm.com> <20191112175523.23145-1-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 Tue, 12 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. > > 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. > > The limit of 65536 bytes can be used by all boards except the Fastlane. The > old driver used a limit of 65532 bytes (0xfffc), which is reintroduced in > this patch. > > Fixes: b7ded0e8b0d1 ("scsi: zorro_esp: Limit DMA transfers to 65535 bytes") > Signed-off-by: Kars de Jong Reviewed-by: Finn Thain > --- > drivers/scsi/zorro_esp.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/drivers/scsi/zorro_esp.c b/drivers/scsi/zorro_esp.c > index ca8e3abeb2c7..a23a8e5794f5 100644 > --- a/drivers/scsi/zorro_esp.c > +++ b/drivers/scsi/zorro_esp.c > @@ -218,7 +218,14 @@ 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; > +} > + > +static u32 fastlane_esp_dma_length_limit(struct esp *esp, u32 dma_addr, > + u32 dma_len) > +{ > + /* The old driver used 0xfffc as limit, so do that here too */ > + return dma_len > 0xfffc ? 0xfffc : dma_len; > } > > static void zorro_esp_reset_dma(struct esp *esp) > @@ -604,7 +611,7 @@ static const struct esp_driver_ops fastlane_esp_ops = { > .esp_write8 = zorro_esp_write8, > .esp_read8 = zorro_esp_read8, > .irq_pending = fastlane_esp_irq_pending, > - .dma_length_limit = zorro_esp_dma_length_limit, > + .dma_length_limit = fastlane_esp_dma_length_limit, > .reset_dma = zorro_esp_reset_dma, > .dma_drain = zorro_esp_dma_drain, > .dma_invalidate = fastlane_esp_dma_invalidate, >