From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Lindgren Subject: Re: [PATCH 1/2] OMAP2+: DMA: Workaround for invalid source position Date: Thu, 3 Nov 2011 14:27:56 -0700 Message-ID: <20111103212756.GZ31337@atomide.com> References: <1320070817-9638-1-git-send-email-peter.ujfalusi@ti.com> <1320070817-9638-2-git-send-email-peter.ujfalusi@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mho-03-ewr.mailhop.org ([204.13.248.66]:42073 "EHLO mho-01-ewr.mailhop.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752089Ab1KCV2F (ORCPT ); Thu, 3 Nov 2011 17:28:05 -0400 Content-Disposition: inline In-Reply-To: <1320070817-9638-2-git-send-email-peter.ujfalusi@ti.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Peter Ujfalusi Cc: Jarkko Nikula , linux-omap@vger.kernel.org, alsa-devel@alsa-project.org * Peter Ujfalusi [111031 06:46]: > If the DMA source position has been asked before the > first actual data transfer has been done, the CSAC > register does not contain valid information. > We can identify this situation by checking the CDAC > register: > CDAC != 0 indicates that the DMA transfer on the channel has > been started already. > When CDAC == 0 we can not trust the CSAC value since it has > not been updated, and can contain random number. > Return the start address in case the DMA has not jet started. > > Note: The CDAC register has been initialized to 0 at dma_start > time. > > Signed-off-by: Peter Ujfalusi > --- > arch/arm/plat-omap/dma.c | 15 +++++++++++++-- > 1 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/plat-omap/dma.c b/arch/arm/plat-omap/dma.c > index c22217c..38b0d44 100644 > --- a/arch/arm/plat-omap/dma.c > +++ b/arch/arm/plat-omap/dma.c > @@ -1024,12 +1024,23 @@ EXPORT_SYMBOL(omap_set_dma_callback); > */ > dma_addr_t omap_get_dma_src_pos(int lch) > { > + u32 cdac; > dma_addr_t offset = 0; > > if (cpu_is_omap15xx()) > offset = p->dma_read(CPC, lch); > - else > - offset = p->dma_read(CSAC, lch); > + else { > + /* > + * CDAC == 0 indicates that the DMA transfer on the channel has > + * not been started (no data has been transferred so far). > + * Return the programmed source start address in this case. > + */ > + cdac = p->dma_read(CDAC, lch); > + if (likely(cdac)) > + offset = p->dma_read(CSAC, lch); > + else > + offset = p->dma_read(CSSA, lch); > + } > > if (IS_DMA_ERRATA(DMA_ERRATA_3_3) && offset == 0) > offset = p->dma_read(CSAC, lch); Should these tests be done only after the errata re-read for both src and dst patches? Otherwise the errata will not be handled? Tony