Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757919Ab3DYMnU (ORCPT ); Thu, 25 Apr 2013 08:43:20 -0400 Received: from mail-ie0-f177.google.com ([209.85.223.177]:60880 "EHLO mail-ie0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756405Ab3DYMnR (ORCPT ); Thu, 25 Apr 2013 08:43:17 -0400 MIME-Version: 1.0 In-Reply-To: <20130425090612.GC4623@gmail.com> References: <1366279934-30761-1-git-send-email-lee.jones@linaro.org> <1366279934-30761-5-git-send-email-lee.jones@linaro.org> <20130425090612.GC4623@gmail.com> Date: Thu, 25 Apr 2013 14:43:16 +0200 Message-ID: Subject: Re: [PATCH 04/32] dmaengine: ste_dma40: Amalgamate DMA source and destination channel numbers From: Linus Walleij To: Lee Jones Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Arnd Bergmann , Linus WALLEIJ , Vinod Koul , Dan Williams , Per Forlin , Rabin Vincent Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6108 Lines: 176 On Thu, Apr 25, 2013 at 11:06 AM, Lee Jones wrote: >> Are we now sacrificing that ability on the altar of simplification? >> >> I actually think not, but that we should do periph-to-periph transfers >> in some other way, and that the .dir attribute should go away from >> the struct stedma40_chan_cfg as well but I'm not entirely sure. >> Someone else? > > Although the DMA40 device supports device-to-device transfers, Linux > does not, so this subject is moot AFAICT. So while there is no active usecase, Linux surely has the ambition to do that as can be seen in: /** * enum dma_transfer_direction - dma transfer mode and direction indicator * @DMA_MEM_TO_MEM: Async/Memcpy mode * @DMA_MEM_TO_DEV: Slave mode & From Memory to Device * @DMA_DEV_TO_MEM: Slave mode & From Device to Memory * @DMA_DEV_TO_DEV: Slave mode & From Device to Device */ enum dma_transfer_direction { DMA_MEM_TO_MEM, DMA_MEM_TO_DEV, DMA_DEV_TO_MEM, DMA_DEV_TO_DEV, DMA_TRANS_NONE, }; I think we need a handshake with Vinod on this. >> If you're doing this change, and after this RX and TX has no semantical >> meaning for these lists, join these two config lists >> into one. > > I agree. See patch: ARM: ux500: Strip out duplicate USB DMA configuration Please squash the applicable portions into this patch then, I don't particularly like fix-later patchstack patterns, it makes series hard to review. >> (...) >> > diff --git a/arch/arm/mach-ux500/usb.c b/arch/arm/mach-ux500/usb.c >> > static u32 d40_chan_has_events(struct d40_chan *d40c) >> > @@ -1744,8 +1740,6 @@ static int d40_validate_conf(struct d40_chan *d40c, >> > struct stedma40_chan_cfg *conf) >> > { >> > int res = 0; >> > - u32 dst_event_group = D40_TYPE_TO_GROUP(conf->dst_dev_type); >> > - u32 src_event_group = D40_TYPE_TO_GROUP(conf->src_dev_type); >> >> Please explain why this is not important to check anymore, I'm not >> following. >> >> > if (conf->dir == STEDMA40_MEM_TO_PERIPH && >> > - dst_event_group == STEDMA40_DEV_DST_MEMORY) { >> > - chan_err(d40c, "Invalid dst\n"); >> > + d40c->base->plat_data->dev_tx[conf->dev_type] == 0 && >> > + d40c->runtime_addr == 0) { >> > + chan_err(d40c, "Invalid TX channel address (%d)\n", >> > + conf->dev_type); >> >> Like here. We are checking for inconsistency between group >> and channel direction, why is it no longer important to check this? > > I'm not entirely sure how this ever worked: > > #define D40_TYPE_TO_GROUP(type) (type / 16) > #define STEDMA40_DEV_DST_MEMORY (-1) > > (dev_type / 16) == -1 > > What number would dev_type have to be for this to be true? -16? No, since it's u32 it cannot really represent negative numbers. This is equivalent: #define D40_TYPE_TO_GROUP(type) (type >> 4) As -1 is 0xffffffff in u32 it will compare at best 0x0fffffff to 0xfffffff. And that is non-attainable. So the line checking event group for == DTEDMA40_DEV_DST_MEMORY should be removed in a separate patch prior to this one, with something like the above as commit message. We cannot really mix that cleanup into this patch... >> > if (conf->dir == STEDMA40_PERIPH_TO_MEM && >> > - src_event_group == STEDMA40_DEV_SRC_MEMORY) { >> > - chan_err(d40c, "Invalid src\n"); >> > - res = -EINVAL; >> > - } > > As above. And same comment. >> > - if (conf->dir == STEDMA40_PERIPH_TO_PERIPH && >> > - (src_event_group != dst_event_group)) { >> > - chan_err(d40c, "Invalid event group\n"); >> > + d40c->base->plat_data->dev_rx[conf->dev_type] == 0 && >> > + d40c->runtime_addr == 0) { >> > + chan_err(d40c, "Invalid RX channel address (%d)\n", >> > + conf->dev_type); >> >> Same here. > > I stopped all 'dev_src/dev_dest' comparisons, as there is only 'dev' now. It is checking for: conf->dir == STEDMA40_PERIPH_TO_PERIPH As we may want to support DEV_TO_DEV at some point. Then no longer, and that is not related to $SUBJECT. >> (...) >> > @@ -2062,7 +2035,7 @@ static int d40_free_dma(struct d40_chan *d40c) >> > { >> > >> > int res = 0; >> > - u32 event; >> > + u32 event = D40_TYPE_TO_EVENT(d40c->dma_cfg.dev_type); >> > struct d40_phy_res *phy = d40c->phy_chan; >> > bool is_src; >> > >> > @@ -2081,13 +2054,11 @@ static int d40_free_dma(struct d40_chan *d40c) >> > } >> > >> > if (d40c->dma_cfg.dir == STEDMA40_MEM_TO_PERIPH || >> > - d40c->dma_cfg.dir == STEDMA40_MEM_TO_MEM) { >> > - event = D40_TYPE_TO_EVENT(d40c->dma_cfg.dst_dev_type); >> > + d40c->dma_cfg.dir == STEDMA40_MEM_TO_MEM) >> >> Why did you just stop checking dma_cfg.dir for == STEDMA40_MEM_TO_MEM >> above? > > That's not what this is doing. STEDMA40_MEM_TO_MEM is still there. > >> And why is dma_cfg.dir suddenly hardcoded to MEM_TO_MEM?? > > It's not. Look again. :) Argh I misread == MEM_TO_MEM for = MEM_TO_MEM ... comparison to assignment. Sorry. >> This seems like a totally unrelated change and should it be done >> it need to be a separate patch with a separate explanation >> AFAICT. >> >> This seems to happen in some other places too, > > If you could point those out, I'll re-evaluate, or explain. I'm after that the change to omit checks for some impossible type/group configs need to be a separate patch. >> and I find it >> very hard to follow the changes here ... can you please consider >> splitting the changes to groups and types semantics into a separate >> patch? > > Can you read the patch again and reconsider please? Yes and now I am even more convinced that the patch needs to be split. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/