+ Adrian On 29 January 2016 at 10:43, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Mon, Dec 21, 2015 at 11:39:56AM +0000, Russell King - ARM Linux wrote: >> This all started with a report from an iMX6 Hummingboard user that >> they were seeing regular "mmc0: Got data interrupt 0x00000002 even >> though no data operation was in progress." messages with 4.4-rc and >> additional patches to enable UHS support in DT for the platform. >> >> When I tested 4.4-rc on an iMX6 Hummingboard with UHS support enabled, >> I found several other issues. This patch series addresses some of >> the issues. >> >> However, while testing on Armada 388, an issue was found there, and >> a fix is also included in this patch set, however it does not depend >> on the rest of the patch series. >> >> We all know that the SDHCI driver is in poor state, and Ulf's desire >> to see it turned into a library (which actually comes from myself.) >> However, with the driver in such a poor state, it makes sense to fix >> a few of the issues first, especially if they result in the code >> shrinking - which they do. >> >> However, given what I've found below, I have to wonder how many of the >> quirks that we have in this driver are down to the poor code rather than >> real hardware problems: how many of them are due to poorly investigated >> bugs. >> >> This series starts off by shutting up some kernel messages that should >> not be verbose: >> - the voltage-ranges DT property is optional, so we should not print >> a message saying that it's missing from DT. That suggests it isn't >> optional. As no ill effect comes from not specifying it, I've >> dropped this message to debug level. >> >> - reworking the voltage-ranges code so that callers know whether the >> optional voltage-ranges property was specified. >> >> - "retrying because a re-tune was needed" - a re-tune is something that >> is part of the higher speed SD specs, and it's required to happen >> periodically. So it's expected and normal behaviour. There's no need >> to print this to the kernel log. >> >> - When tuning fails, rather than a bland "mmc0: tuning execution failed" >> message, print the error code so that we can see what the reason for >> the failure is. MMC fails on this point in many places. >> >> - Move the initialisation of the command ->error member. It looks to >> me as if this is not required; mmc_start_request() does this already, >> as it seems the rest of the MMC core does too. Maybe this should be >> removed altogether? >> >> - Testing error bits, then setting the error, then testing the error >> value, and completing the command is a very lengthy way to deal with >> errors here. Test the error bits, and then decide what error occurred >> before completing. (This code is actually buggy, see the next change). >> >> - If a command _response_ CRC error occurs, we can't be certain whether >> the card received the command successfully, and has started processing >> it. If it has, and it results in data being read from the card, the >> card will enter data transfer state, and start sending data to the >> host. Therefore, it is completely wrong to blindly terminate the >> command, especially when such termination fails to clean _anything_ >> up - eg, it leaves DMA in place so the host can continue DMAing to the >> memory, and it leaves buffers DMA mapped - which eventually annoys the >> DMA API debugging. Fix this by assuming that a CRC error is a receive >> side error. If the card did not correctly receive the command, it >> will not initiate a data transfer, and we should time out after the >> card specified timeout. >> >> With the unmodified mainline code, even if we reset the state machines >> when finishing a request in error, the _card_ itself may well still be >> in data transfer mode when this happens. How can we be sure what state >> the data side is actually in? Could this be why (eg) sdhci-esdhc-imx.c >> has this: >> >> /* FIXME: delay a bit for card to be ready for next tuning due to errors */ >> mdelay(1); >> >> And how many more such _hacks_ are working around similar problems? >> >> - The unaligned buffer handling is a total waste of resources in its >> current form. We DMA map, sync, and unmap it on every transfer, >> whether the buffer is used or not. For MMC/SD transfers, these will >> be coming from the VFS/MM layers, which operate through the page >> cache - hence the vast majority of buffers will be page aligned. >> Performance measurements on iMX6 show that this additional DMA >> maintanence is responsible for a 10% reduction in read transfer >> performance. Switch this to use a DMA coherent mapping instead, which >> needs no DMA maintanence. >> >> - sdhci_adma_table_post() is badly coded: we walk the scatterlist >> looking for any buffers which might not be aligned (which can be a >> rare event, see above) and then we only do something if we find an >> unaligned buffer _and_ it's a read transfer. So for a write transfer, >> this scatterlist walking is a total waste of CPU cycles. Testing the >> transfer direction is much cheaper than walking the scatterlist. >> Re-organise the code to do the cheap test first. >> >> - There are two paths to identical DMA unmapping code (the code around >> dma_unmap_sg()) in sdhci_finish_data() and its child function >> sdhci_adma_table_post(). Trivially simplify this duplication. >> >> - Move sdhci_pre_dma_transfer() so we avoid needing to declare it. >> >> - Do the same thing with sdhci_prepare_data() and sdhci_pre_dma_transfer() >> as with sdhci_finish_data() and sdhci_adma_table_post(). >> >> - Fix the mess that is the data segment host_cookie handling. The >> existing code seems like a candidate for the obfuscated coding prize! >> Four patches address this, turning it into something much easier to >> understand, which then allows (finally)... >> >> - The DMA API leak which occurs when we have mapped the DMA buffers in >> sdhci_prepare_data() and an error occurs early on in the processing >> of a request. >> >> - A change (mentioned above) which fixes a prior commit for Armada 38x >> using sdhci-pxav3.c, found while trying to get the higher speed modes >> working on these SoCs. Clearly the existing code is broken, this at >> least resolves some of the breakage by allowing the correct high-order >> SDHCI capabilities through. >> >> - Fixing another DMA API leak with the pre/post request handling, where >> a current request can change the state of the SDHCI_REQ_USE_DMA, and >> thus stop a mapped request being unmapped. >> >> - Fixing the SDHCI timeout calculation code to correctly round timeouts >> up rather than down, and correctly calculate the time (in microseconds) >> for a certain number of card clocks. >> >> - Consolidating the SDHCI address/size alignment handling so we only walk >> the scatterlist once instead of twice. >> >> Further patches are necessary as there are still a number of observable >> problems when using this driver on iMX6 with UHS cards. Patches up to >> and including "mmc: sdhci: further fix for DMA unmapping in >> sdhci_post_req()" should be considered for inclusion in the stable >> kernel trees. >> >> I've tested these changes on iMX6 at UHS speeds, and Armada 388 SoCs >> at HS speeds so far. Others should test them. > > One comment from Adrian addressed. > > drivers/mmc/card/block.c | 4 +- > drivers/mmc/core/core.c | 17 +- > drivers/mmc/host/sdhci-pxav3.c | 6 +- > drivers/mmc/host/sdhci.c | 444 ++++++++++++++++++----------------------- > drivers/mmc/host/sdhci.h | 4 +- > 5 files changed, 213 insertions(+), 262 deletions(-) > > -- > RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up > according to speedtest.net. I have applied patch 1 to 4, for next! The rest are sdhci patches, which from now on needs acks from Adrian for me to pick them up. Thanks and kind regards! Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
