Hi all, I have looked over the DMA residue branches in renesas-drivers tree (topic/rcar-dmac-hamza-v3 and topic/rcar-dmac-residue-v1) hoping to bring them to upstream. The original author for the bulk of the patches Hamza Farooq have not shown any activity since autumn 2015. In this cover letter I talk about all the patches in the above branches but for obvious reasons only patches I think should be forwarded to upstream are included in the series. All patches are based ontop of v4.7-rc1 and are tested on Koelsch using Geerts sertest tool to generate DMA traffic. The highest baud I could get to work at was 921600 bps. >From reading the original mail threads my conclusion is that this is good enough since all errors reported by Hamza Farooq where related to the serial sh-sci driver. * Patches from topic/rcar-dmac-hamza-v3 - dma: rcar-dma: add wait after stopping dma engine In a perfect world one should check that RCAR_DMACHCR_DE is read back as 0 after it have been cleared. The documentation clearly states that one should do so. In the real world the worst case time for this register to be cleared as Morimoto-san checked with HW is 700us. Laurent later pointed out this is too long to busy loop over since this is done from both interrupt context and user context with a spinlock hold. Also in the real world the rcar-dmac driver WARN_ON_ONCE() that RCAR_DMACHCR_DE is not set before it attempts to start an transferee in rcar_dmac_chan_start_xfer(). So if this ever becomes a problem we will know about it. At least I have never seen this warning while using DMA. Whit this in mind I have not tried to implement a fix for this and I think the original patch can be dropped. - dma: rcar-dma: Added dma_pause operation to rcar_dma driver This patch adds support for device pause operation, but not the resume operation. As pointed out in the original mail thread the pausing must not destroy any already started transaction which it do in its current form according to its author. Since the feature is incomplete and the use case never documented I propose we drop this patch and if we can find the use case create a separate task to add pause/resume functionality to the driver later. - dma: rcar-dma: check if complete DMA packet received but not processed This patch is already addressed by Laruent in the original maling thread: "I don't think this will work. In particular rcar_dmac_tx_status() can be called with a cookie corresponding to a transfer not yet scheduled. A pending transfer complete interrupt doesn't mean that that cookie is complete. Furthermore I'm not sure this will really improve performances. The dma_cookie_status() call below just compares cookie values, I don't expect it to be much slower than a register read." I can see no reason to disagree with Laruent here and I propose this patch is dropped. - dma: rcar-dma: use result of updated get_residue in tx_status Patch is IMHO good but needs a explanation in commit message to address the questions raised in the original mail thread. I have added en explanation and included the original patch. - dma: rcar-dma: warn if transfer cannot start as TE = 1 Patch is a bit oddly implemented and uses new functionality from patch 'dma: rcar-dma: add wait after stopping dma engine' above. I do however think the patch have merit. One should make sure according to the documentation that RCAR_DMACHCR_TE is not set before starting a transfer. I have reworked the check and proposed a different solution. - dma: rcar-dma: Fixed active descriptor initializing Patch is clearly a bugfix and looks good. Laurent had a good comment in the original mail thread about how it can be made differently by reworking rcar_dmac_free_chan_resources() to call rcar_dmac_chan_reinit() which would correctly set rchan->desc.running to NULL. I have tried to implement this but failed. In my attempts to implement Laurents proposal which I thought would be trivial the kernel locks-up after a while with 'rcu_sched self-detected stall on CPU'. And I'm not smart enough to figure out why so I have kept the original patch so the bug fix part can be merged since that in itself is good. * Patch from topic/rcar-dmac-residue-v1 - dmaengine: rcar-dmac: Fix residue reporting for pending descriptors Patch is good AFIK. There where one report on the maling list by Hamza Farooq that state he saw lots of warnings coming from the WARN() introduced in this patch. I have run lots of testes using Geers nice sertest tool and have not once seen the warning once. The patch is included in this series. Laurent Pinchart (1): dmaengine: rcar-dmac: Fix residue reporting for pending descriptors Muhammad Hamza Farooq (2): dma: rcar-dma: use result of updated get_residue in tx_status dma: rcar-dma: Fixed active descriptor initializing Niklas Söderlund (1): dmaengine: rcar-dmac: warn if transfer cannot start as TE = 1 drivers/dma/sh/rcar-dmac.c | 40 +++++++++++++++++++++++++++++++++++++--- 1 file changed, 37 insertions(+), 3 deletions(-) -- 2.8.3