> -----Original Message----- > From: Frieder Schrempf [mailto:frieder.schrempf@xxxxxxxxxx] > Sent: Thursday, February 25, 2021 4:23 PM > To: Abel Vesa <abel.vesa@xxxxxxx>; Dong Aisheng <dongas86@xxxxxxxxx> > Cc: Aisheng Dong <aisheng.dong@xxxxxxx>; Rob Herring <robh@xxxxxxxxxx>; > Peng Fan <peng.fan@xxxxxxx>; Jacky Bai <ping.bai@xxxxxxx>; Anson Huang > <anson.huang@xxxxxxx>; devicetree <devicetree@xxxxxxxxxxxxxxx>; > Stephen Boyd <sboyd@xxxxxxxxxx>; Shawn Guo <shawnguo@xxxxxxxxxx>; > Mike Turquette <mturquette@xxxxxxxxxxxx>; Linux Kernel Mailing List > <linux-kernel@xxxxxxxxxxxxxxx>; Marek Vasut <marek.vasut@xxxxxxxxx>; > dl-linux-imx <linux-imx@xxxxxxx>; Sascha Hauer <kernel@xxxxxxxxxxxxxx>; > Fabio Estevam <fabio.estevam@xxxxxxx>; Philipp Zabel > <p.zabel@xxxxxxxxxxxxxx>; Adam Ford <aford173@xxxxxxxxx>; linux-clk > <linux-clk@xxxxxxxxxxxxxxx>; moderated list:ARM/FREESCALE IMX / MXC > ARM ARCHITECTURE <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; Lucas Stach > <l.stach@xxxxxxxxxxxxxx> > Subject: Re: [PATCH v5 10/14] clk: imx: Add generic blk-ctl driver > > Hi Abel, > > On 17.11.20 15:48, Abel Vesa wrote: > > On 20-11-11 17:13:25, Dong Aisheng wrote: > >> On Tue, Nov 3, 2020 at 7:22 PM Abel Vesa <abel.vesa@xxxxxxx> wrote: > >> ... > >>> +static int imx_blk_ctl_reset_set(struct reset_controller_dev *rcdev, > >>> + unsigned long id, bool assert) { > >>> + struct imx_blk_ctl_drvdata *drvdata = container_of(rcdev, > >>> + struct imx_blk_ctl_drvdata, rcdev); > >>> + unsigned int offset = drvdata->rst_hws[id].offset; > >>> + unsigned int shift = drvdata->rst_hws[id].shift; > >>> + unsigned int mask = drvdata->rst_hws[id].mask; > >>> + void __iomem *reg_addr = drvdata->base + offset; > >>> + unsigned long flags; > >>> + u32 reg; > >>> + > >>> + if (!assert && !test_bit(1, &drvdata->rst_hws[id].asserted)) > >>> + return -ENODEV; > >> > >> What if consumers call deassert first in probe which seems common in > kernel? > >> It seems will fail. > >> e.g. > >> probe() { > >> reset_control_get() > >> reset_control_deassert() > >> } > >> > >> Regards > >> Aisheng > >> > > > > OK, I'm trying to explain here how I know the resets are supposed to > > be working and how the BLK_CTL IP is working. > > > > > > First of, the BLK_CTL bits (resets and clocks) all have the HW init > > (default) values as 0. Basically, after the blk_ctl PD is powered on, > > the resets are deasserted and clocks are gated by default. Since the > > blk_ctl is not the parent of any of the consumers in devicetree (the > > reg maps are entirely different anyway), there is no way of ordering > > the runtime callbacks between the consumer and the blk_ctl. So we > > might end up having the runtime resume callback after the one from > > EARC (consumer), for example, which will basically overwrite the value > written by EARC driver with whatever was saved on suspend. > > > > Now, about the usage of the reset bits. AFAICT, it would make more > > sense to assert the reset, then enable the clock, then deassert. This > > way, you're keeping the EARC (consumer) in reset (with the clocks on) > > until you eventually release it out of reset by deasserting. This is > > how the runtime resume should deal with the reset and the clock. As > > for the runtime suspend, the reset can be entirely ignored as long as you're > disabling the clock. > > > > This last part will allow the blk_ctl to make the following assumption: > > if all the clocks are disabled and none of the reset bits are asserted, I can > power off. > > > > Now, I know there are drivers outthere that do assert on suspend, but > > as long as the clocks are disabled, the assert will have no impact. > > But maybe in their case the reset controller cannot power down itself. > > > > As for the safekeeping of the register, I'll just drop it due to the following > arguments: > > 1. all the clocks are gated by default 2. all resets are deasserted by > > default 3. when blk_ctl goes down, all the consumers go down. (all > > have the same PD) > > > > From 1 and 2 results the IP will not be running and from 3 results > > the HW state of every IP becomes HW init state. > > Are there any plans to continue this work? As BLK-CTL it is not only relevant > for the i.MX8MP, but also for i.MX8MM and i.MX8MN, it would be nice to get > this ready in order to prepare for proper graphics/display support. > Before continuing this work, we need to find out a way to resolve the cycling dependency issue between power domain and blk-ctrl. it is indeed introduced some troubles in NXP latest internal release when the blk-ctrl driver is added. BR Jacky Bai > Thanks > Frieder
