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. -- 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
