From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sekhar Nori Subject: Re: [PATCH 2/6] ARM: DTS: da850: Use the new DT bindings for the eDMA3 Date: Tue, 15 Dec 2015 20:50:35 +0530 Message-ID: <56702FC3.5050705@ti.com> References: <1449237210-16381-1-git-send-email-peter.ujfalusi@ti.com> <1449237210-16381-3-git-send-email-peter.ujfalusi@ti.com> <566FDF93.7050005@ti.com> <566FFD1C.4080000@ti.com> <56701A47.9090105@ti.com> <56701E2C.7060308@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <56701E2C.7060308-l0cyMroinI0@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Peter Ujfalusi Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, khilman-1D3HCaltpLuhEniVeURVKkEOCMrvLtNR@public.gmane.org List-Id: devicetree@vger.kernel.org On Tuesday 15 December 2015 07:35 PM, Peter Ujfalusi wrote: > On 12/15/2015 03:48 PM, Sekhar Nori wrote: >>>> In future, if/when we gain QDMA support, the QDMA channels could be used >>>> for memcopy. >>> >>> Well, in short there is no way to get the qDMA working in a different way >>> either. qDMA channel is in essence using 'normal' eDMA channel. This means >>> that we still need to reserve the eDMA channel to be used for memcpy, but >>> instead of SW triggering it (as we do it right now), we would need to use the >>> channel as qDMA and set things up accordingly. I don't really see the benefit >>> for qDMA mode to be honest. >> >> I guess the only advantage is that they will not clash with peripheral >> mode usage. But even then, some sort of reservation is needed. So I >> guess QDMA is no better than the EDMA reserved channels? > > It will clash with the peripheral mode use since it needs to take one of the > eDMA channels. qDMA mode is basically differs from the mode we are using by > how the channel is triggered. Currently we start the memcpy with SW trigger. Alright, so I was missing this detail. Thanks for clarifying it on IRC. The EDMA specification makes it look like 8 additional QDMA channels can be used over 32 DMA channels, but in reality they are not additional channels since TCC is only valid between 0-31. So, I agree. QDMA does not buy us any parallel transfers. Thanks, Sekhar -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html