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=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 88118C31E44 for ; Fri, 14 Jun 2019 05:27:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6567A20851 for ; Fri, 14 Jun 2019 05:27:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726103AbfFNF1f (ORCPT ); Fri, 14 Jun 2019 01:27:35 -0400 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:55796 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725767AbfFNF1e (ORCPT ); Fri, 14 Jun 2019 01:27:34 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id 975A2293CA; Fri, 14 Jun 2019 01:27:27 -0400 (EDT) Date: Fri, 14 Jun 2019 15:27:36 +1000 (AEST) From: Finn Thain To: Ming Lei , "Juergen E . Fischer" cc: linux-scsi@vger.kernel.org, "Martin K . Petersen" , James Bottomley , Bart Van Assche , Hannes Reinecke , Christoph Hellwig , Jim Gill , Cathy Avery , "Ewan D . Milne" , Brian King , James Smart , Michael Schmitz , Greg Kroah-Hartman , devel@driverdev.osuosl.org, linux-usb@vger.kernel.org, Dan Carpenter , Benjamin Block Subject: Re: [PATCH V3 10/15] scsi: aha152x: use sg helper to operate scatterlist In-Reply-To: <20190614025316.7360-11-ming.lei@redhat.com> Message-ID: References: <20190614025316.7360-1-ming.lei@redhat.com> <20190614025316.7360-11-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Hi Ming, On Fri, 14 Jun 2019, Ming Lei wrote: > Use the scatterlist iterators and remove direct indexing of the > scatterlist array. > > This way allows us to pre-allocate one small scatterlist, which can be > chained with one runtime allocated scatterlist if the pre-allocated one > isn't enough for the whole request. > > Signed-off-by: Ming Lei > --- > drivers/scsi/aha152x.c | 29 +++++++++++++++++++---------- > 1 file changed, 19 insertions(+), 10 deletions(-) > > diff --git a/drivers/scsi/aha152x.c b/drivers/scsi/aha152x.c > index 97872838b983..bc9d12aa7880 100644 > --- a/drivers/scsi/aha152x.c > +++ b/drivers/scsi/aha152x.c > @@ -2033,7 +2033,7 @@ static void datai_run(struct Scsi_Host *shpnt) > CURRENT_SC->SCp.buffers_residual > 0) { > /* advance to next buffer */ > CURRENT_SC->SCp.buffers_residual--; > - CURRENT_SC->SCp.buffer++; > + CURRENT_SC->SCp.buffer = sg_next(CURRENT_SC->SCp.buffer); > CURRENT_SC->SCp.ptr = SG_ADDRESS(CURRENT_SC->SCp.buffer); > CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length; > } > @@ -2139,7 +2139,7 @@ static void datao_run(struct Scsi_Host *shpnt) > if(CURRENT_SC->SCp.this_residual==0 && CURRENT_SC->SCp.buffers_residual>0) { > /* advance to next buffer */ > CURRENT_SC->SCp.buffers_residual--; > - CURRENT_SC->SCp.buffer++; > + CURRENT_SC->SCp.buffer = sg_next(CURRENT_SC->SCp.buffer); > CURRENT_SC->SCp.ptr = SG_ADDRESS(CURRENT_SC->SCp.buffer); > CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length; > } > @@ -2160,20 +2160,29 @@ static void datao_end(struct Scsi_Host *shpnt) > if(TESTLO(DMASTAT, DFIFOEMP)) { > int data_count = (DATA_LEN - scsi_get_resid(CURRENT_SC)) - > GETSTCNT(); data_count appears to be the number of bytes remaining in the FIFO. (I have to infer that much from the surrounding code. I don't have documentation for this controller.) Some comments would be nice. > + struct scatterlist *sg = scsi_sglist(CURRENT_SC); > + int left, i = 0; > > CMD_INC_RESID(CURRENT_SC, data_count); > Apparently the aim is to increase the residual by the number of bytes that will never leave the FIFO. Above we can see that increase performed by scsi_set_resid() and now the same has to be done to the SCp struct. > data_count -= CURRENT_SC->SCp.ptr - > SG_ADDRESS(CURRENT_SC->SCp.buffer); Here, data_count effectively has SCp.this_residual subtracted from it. > - while(data_count>0) { > - CURRENT_SC->SCp.buffer--; > - CURRENT_SC->SCp.buffers_residual++; > - data_count -= CURRENT_SC->SCp.buffer->length; > - } So far, so good. > - CURRENT_SC->SCp.ptr = SG_ADDRESS(CURRENT_SC->SCp.buffer) - > - data_count; > - CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length + > - data_count; This is like saying ptr = buffer + residual, which is bogus. This must be an old bug, but we never hit it because the FIFO is always empty when we get a DISCONNECT message. Probably because every SG segment has a length that is a multiple of 128 bytes. (Juergen?) > + > + left = CURRENT_SC->transfersize - data_count; Are you sure about that? Perhaps you meant to write, left = scsi_bufflen(CURRENT_SC) - scsi_get_resid(CURRENT_SC); Is there a better name for this variable? Maybe 'sent' or 'bytes_sent'? > + for (i = 0; left > 0 && !sg_is_last(sg); i++, sg = sg_next(sg)) { > + if (left < sg->length) > + break; > + left -= sg->length; > + } > + > + if (data_count > 0) { > + CURRENT_SC->SCp.buffers_residual += i; Shouldn't that be, CURRENT_SC->SCp.buffers_residual = i; > + CURRENT_SC->SCp.buffer = sg; > + > + CURRENT_SC->SCp.ptr = SG_ADDRESS(CURRENT_SC->SCp.buffer) + left; > + CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length - > + left; > + } > } > > SETPORT(SXFRCTL0, CH1|CLRCH1|CLRSTCNT); > BTW, datao_run() seems to guarantee that the FIFO will never contain more than min(128, SCp.this_residual) so I suspect that this code can be simplified. That's just BTW. I wouldn't attempt to optimize this branch as it will only run when the FIFO is not empty, if ever. So I'd prefer clarity. Besides, I don't have the hardware to test it on. --