From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752621AbbJOLFk (ORCPT ); Thu, 15 Oct 2015 07:05:40 -0400 Received: from arroyo.ext.ti.com ([192.94.94.40]:44600 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751514AbbJOLFj (ORCPT ); Thu, 15 Oct 2015 07:05:39 -0400 Subject: Re: [PATCH] ARM: edma: special case slot limit workaround To: John Ogness , References: <87eggws90a.fsf@linutronix.de> CC: , , Vinod Koul , "Nori, Sekhar" From: Peter Ujfalusi X-Enigmail-Draft-Status: N1110 Message-ID: <561F8860.4030507@ti.com> Date: Thu, 15 Oct 2015 14:05:04 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <87eggws90a.fsf@linutronix.de> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/15/2015 01:48 PM, John Ogness wrote: > Currently drivers are limited to 19 slots for cyclic transfers. > However, if the DMA burst size is the same as the period size, > the period size can be changed to the full buffer size and > intermediate interrupts activated. Since intermediate interrupts > will trigger for each burst and the burst size is the same as > the period size, the driver will get interrupts each period as > expected. This has the benefit of allowing the functionality of > many more slots, but only uses 2 slots. > > This workaround is only active if more than 19 slots are needed > and the burst size matches the period size. To: Vinod CC: l-o, Sekhar at least > > Signed-off-by: John Ogness > --- > drivers/dma/edma.c | 25 ++++++++++++++++++++++--- > 1 file changed, 22 insertions(+), 3 deletions(-) > > diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c > index 493c774..16bd193 100644 > --- a/drivers/dma/edma.c > +++ b/drivers/dma/edma.c > @@ -585,6 +585,7 @@ static struct dma_async_tx_descriptor *edma_prep_dma_cyclic( > struct edma_desc *edesc; > dma_addr_t src_addr, dst_addr; > enum dma_slave_buswidth dev_width; > + bool use_intermediate = false; > u32 burst; > int i, ret, nslots; > > @@ -626,8 +627,21 @@ static struct dma_async_tx_descriptor *edma_prep_dma_cyclic( > * but the synchronization is difficult to achieve with Cyclic and > * cannot be guaranteed, so we error out early. > */ > - if (nslots > MAX_NR_SG) > - return NULL; > + if (nslots > MAX_NR_SG) { > + /* > + * If the burst and period sizes are the same, we can put > + * the full buffer into a single period and activate > + * intermediate interrupts. This will produce interrupts > + * after each burst, which is also after each desired period. > + */ > + if (burst == period_len) { > + period_len = buf_len; > + nslots = 2; > + use_intermediate = true; > + } else { > + return NULL; > + } > + } > > edesc = kzalloc(sizeof(*edesc) + nslots * > sizeof(edesc->pset[0]), GFP_ATOMIC); > @@ -706,8 +720,13 @@ static struct dma_async_tx_descriptor *edma_prep_dma_cyclic( > /* > * Enable period interrupt only if it is requested > */ > - if (tx_flags & DMA_PREP_INTERRUPT) > + if (tx_flags & DMA_PREP_INTERRUPT) { > edesc->pset[i].param.opt |= TCINTEN; > + > + /* Also enable intermediate interrupts if necessary */ > + if (use_intermediate) > + edesc->pset[i].param.opt |= ITCINTEN; > + } > } The workaround looks fine, but please rebase it on the latest edma code from linux-next. -- Péter