On Tue, Nov 12, 2019 at 09:46:33AM +0530, Anup Patel wrote: > On Mon, Nov 11, 2019 at 10:50 PM Paul Walmsley <paul@xxxxxxxxx> wrote: > > > > On Mon, 11 Nov 2019, Christoph Hellwig wrote: > > > > > On Mon, Nov 11, 2019 at 05:06:24PM +0530, Anup Patel wrote: > > > > We really don't need this driver. Instead, we can simply re-use > > > > following drivers: > > > > mfd/syscon > > > > power/reset/syscon-reboot > > > > power/reset/syscon-poweroff > > > > > > > > Just enable following to your defconfig: > > > > CONFIG_POWER_RESET=y > > > > CONFIG_POWER_RESET_SYSCON=y > > > > CONFIG_POWER_RESET_SYSCON_POWEROFF=y > > > > CONFIG_SYSCON_REBOOT_MODE=y > > > > > > > > > > > > Once above drivers are enabled in your defconfig, make sure > > > > test device DT nodes are described in the following way for virt machine: > > > > > > Oh well, that is a lot more churn than a just works driver, and > > > will also pull it dependencies like regmap which quite blow up the > > > kernel size. But I guess that is where modern Linux drivers are > > > heading, so I'm not going to complain too loud.. > > > > The core issue is that putting random register writes in DT doesn't match > > the hardware. And the doctrine with DT has always been that it's supposed > > to represent the actual hardware. On FPGA bitstreams or ASICs that have > > the teststatus/testfinisher IP block, there really is an IP block out > > there - it's not just a bare register. > > > > If you update your driver to note that this is a SiFive IP block rather > > than a "RISC-V" IP block, I'll ack it. > > > > The SiFive Test device has only one register at offset 0x0 and three > possible magic values (0x3333, 0x5555, and 0x7777). > > The SYSCON based Reboot and Poweroff driver do exactly the same > thing what Christop's virt machine poweroff driver does so we are not > doing "random register writes" via DT. > > In fact, using SYSCON based Reboot and Poweroff we are actually > describing the Reboot and Poweroff mechanism directly in DT without > adding a complete driver for just one register write. This means we > are totally aligned with "DT doctrine" and over here we going one-step > more by describing Reboot and Poweroff mechanism in DT. > > A quick GREP shows that the SYSCON Reboot and Poweroff drivers > are quite widely used in ARM, ARM64 and MIPS architectures. Some of > the SOCs using these drivers are: Samsung Exynos, HiSilicon Hi3660, > HiSilicon Hi6220, Rockchip RK3xxx, AppliedMicro XGene, Broadcom > BCM33xx, Broadcom BCM63xx, etc. Majority of ARM/ARM64 SOCs > these days use the PSCI based SYSTEM RESET and SHUTDOWN > methods so we might not see more Reboot and Poweroff drivers for > ARM world. > > IMHO, we should definitely avoid adding a driver to Linux when there > a generic driver already available. This helps in kernel maintenance > in long-term. I guess I should have finished reading the thread... I agree with both of you. :) The DT binding should match the h/w as Paul says. However, a h/w specific binding can easily map to a generic driver if a given client OS has one. That probably hasn't been done yet for syscon-poweroff, but should. Rob
