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authorLinus Torvalds <torvalds@linux-foundation.org>2018-04-02 20:20:12 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-02 20:20:12 -0700
commitf5a8eb632b562bd9c16c389f5db3a5260fba4157 (patch)
tree82687234d772ff8f72a31e598fe16553885c56c9 /Documentation/blackfin/bfin-spi-notes.txt
parentc9297d284126b80c9cfd72c690e0da531c99fc48 (diff)
parentdd3b8c329aa270027fba61a02a12600972dc3983 (diff)
Merge tag 'arch-removal' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic
Pul removal of obsolete architecture ports from Arnd Bergmann: "This removes the entire architecture code for blackfin, cris, frv, m32r, metag, mn10300, score, and tile, including the associated device drivers. I have been working with the (former) maintainers for each one to ensure that my interpretation was right and the code is definitely unused in mainline kernels. Many had fond memories of working on the respective ports to start with and getting them included in upstream, but also saw no point in keeping the port alive without any users. In the end, it seems that while the eight architectures are extremely different, they all suffered the same fate: There was one company in charge of an SoC line, a CPU microarchitecture and a software ecosystem, which was more costly than licensing newer off-the-shelf CPU cores from a third party (typically ARM, MIPS, or RISC-V). It seems that all the SoC product lines are still around, but have not used the custom CPU architectures for several years at this point. In contrast, CPU instruction sets that remain popular and have actively maintained kernel ports tend to all be used across multiple licensees. [ See the new nds32 port merged in the previous commit for the next generation of "one company in charge of an SoC line, a CPU microarchitecture and a software ecosystem" - Linus ] The removal came out of a discussion that is now documented at https://lwn.net/Articles/748074/. Unlike the original plans, I'm not marking any ports as deprecated but remove them all at once after I made sure that they are all unused. Some architectures (notably tile, mn10300, and blackfin) are still being shipped in products with old kernels, but those products will never be updated to newer kernel releases. After this series, we still have a few architectures without mainline gcc support: - unicore32 and hexagon both have very outdated gcc releases, but the maintainers promised to work on providing something newer. At least in case of hexagon, this will only be llvm, not gcc. - openrisc, risc-v and nds32 are still in the process of finishing their support or getting it added to mainline gcc in the first place. They all have patched gcc-7.3 ports that work to some degree, but complete upstream support won't happen before gcc-8.1. Csky posted their first kernel patch set last week, their situation will be similar [ Palmer Dabbelt points out that RISC-V support is in mainline gcc since gcc-7, although gcc-7.3.0 is the recommended minimum - Linus ]" This really says it all: 2498 files changed, 95 insertions(+), 467668 deletions(-) * tag 'arch-removal' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic: (74 commits) MAINTAINERS: UNICORE32: Change email account staging: iio: remove iio-trig-bfin-timer driver tty: hvc: remove tile driver tty: remove bfin_jtag_comm and hvc_bfin_jtag drivers serial: remove tile uart driver serial: remove m32r_sio driver serial: remove blackfin drivers serial: remove cris/etrax uart drivers usb: Remove Blackfin references in USB support usb: isp1362: remove blackfin arch glue usb: musb: remove blackfin port usb: host: remove tilegx platform glue pwm: remove pwm-bfin driver i2c: remove bfin-twi driver spi: remove blackfin related host drivers watchdog: remove bfin_wdt driver can: remove bfin_can driver mmc: remove bfin_sdh driver input: misc: remove blackfin rotary driver input: keyboard: remove bf54x driver ...
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-SPI Chip Select behavior:
-
-With the Blackfin on-chip SPI peripheral, there is some logic tied to the CPHA
-bit whether the Slave Select Line is controlled by hardware (CPHA=0) or
-controlled by software (CPHA=1). However, the Linux SPI bus driver assumes that
-the Slave Select is always under software control and being asserted during
-the entire SPI transfer. - And not just bits_per_word duration.
-
-In most cases you can utilize SPI MODE_3 instead of MODE_0 to work-around this
-behavior. If your SPI slave device in question requires SPI MODE_0 or MODE_2
-timing, you can utilize the GPIO controlled SPI Slave Select option instead.
-In this case, you should use GPIO based CS for all of your slaves and not just
-the ones using mode 0 or 2 in order to guarantee correct CS toggling behavior.
-
-You can even use the same pin whose peripheral role is a SSEL,
-but use it as a GPIO instead.