diff options
Diffstat (limited to 'target/linux/apm821xx/patches-4.4/030-usb-dwc2-endian-fix.patch')
| -rw-r--r-- | target/linux/apm821xx/patches-4.4/030-usb-dwc2-endian-fix.patch | 95 |
1 files changed, 95 insertions, 0 deletions
diff --git a/target/linux/apm821xx/patches-4.4/030-usb-dwc2-endian-fix.patch b/target/linux/apm821xx/patches-4.4/030-usb-dwc2-endian-fix.patch new file mode 100644 index 0000000000..9078b6c351 --- /dev/null +++ b/target/linux/apm821xx/patches-4.4/030-usb-dwc2-endian-fix.patch @@ -0,0 +1,95 @@ +From: Arnd Bergmann <arnd@arndb.de> +Subject: [PATCH v4] usb: dwc2: fix regression on big-endian PowerPC/ARM systems +Date: Fri, 13 May 2016 15:52:27 +0200 +Message-Id: <1463147559-544140-1-git-send-email-arnd@arndb.de> + +A patch that went into Linux-4.4 to fix big-endian mode on a Lantiq +MIPS system unfortunately broke big-endian operation on PowerPC +APM82181 as reported by Christian Lamparter, and likely other +systems. + +It actually introduced multiple issues: + +- it broke big-endian ARM kernels: any machine that was working + correctly with a little-endian kernel is no longer using byteswaps + on big-endian kernels, which clearly breaks them. +- On PowerPC the same thing must be true: if it was working before, + using big-endian kernels is now broken. Unlike ARM, 32-bit PowerPC + usually uses big-endian kernels, so they are likely all broken. +- The barrier for dwc2_writel is on the wrong side of the __raw_writel(), + so the MMIO no longer synchronizes with DMA operations. +- On architectures that require specific CPU instructions for MMIO + access, using the __raw_ variant may turn this into a pointer + dereference that does not have the same effect as the readl/writel. + +This patch is a simple revert for all architectures other than MIPS, +in the hope that we can more easily backport it to fix the regression +on PowerPC and ARM systems without breaking the Lantiq system again. + +We should follow this up with a more elaborate change to add runtime +detection of endianness, to make sure it also works on all other +combinations of architectures and implementations of the usb-dwc2 +device. That patch however will be fairly large and not appropriate +for backports to stable kernels. + +Felipe suggested a different approach, using an endianness switching +register to always put the device into LE mode, but unfortunately +the dwc2 hardware does not provide a generic way to do that. Also, +I see no practical way of addressing the problem more generally by +patching architecture specific code on MIPS. + +Signed-off-by: Arnd Bergmann <arnd@arndb.de> +Fixes: 95c8bc360944 ("usb: dwc2: Use platform endianness when accessing registers") +--- + drivers/usb/dwc2/core.h | 27 +++++++++++++++++++++++++++ + 1 file changed, 27 insertions(+) + +diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h +index 3c58d633ce80..dec0b21fc626 100644 +--- a/drivers/usb/dwc2/core.h ++++ b/drivers/usb/dwc2/core.h +@@ -64,6 +64,17 @@ + DWC2_TRACE_SCHEDULER_VB(pr_fmt("%s: SCH: " fmt), \ + dev_name(hsotg->dev), ##__VA_ARGS__) + ++#ifdef CONFIG_MIPS ++/* ++ * There are some MIPS machines that can run in either big-endian ++ * or little-endian mode and that use the dwc2 register without ++ * a byteswap in both ways. ++ * Unlike other architectures, MIPS apparently does not require a ++ * barrier before the __raw_writel() to synchronize with DMA but does ++ * require the barrier after the __raw_writel() to serialize a set of ++ * writes. This set of operations was added specifically for MIPS and ++ * should only be used there. ++ */ + static inline u32 dwc2_readl(const void __iomem *addr) + { + u32 value = __raw_readl(addr); +@@ -90,6 +101,22 @@ static inline void dwc2_writel(u32 value, void __iomem *addr) + pr_info("INFO:: wrote %08x to %p\n", value, addr); + #endif + } ++#else ++/* Normal architectures just use readl/write */ ++static inline u32 dwc2_readl(const void __iomem *addr) ++{ ++ return readl(addr); ++} ++ ++static inline void dwc2_writel(u32 value, void __iomem *addr) ++{ ++ writel(value, addr); ++ ++#ifdef DWC2_LOG_WRITES ++ pr_info("info:: wrote %08x to %p\n", value, addr); ++#endif ++} ++#endif + + /* Maximum number of Endpoints/HostChannels */ + #define MAX_EPS_CHANNELS 16 +-- +2.7.0 + + |