From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 72EB52233B; Fri, 10 May 2024 10:19:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715336391; cv=none; b=PAHn4JeJywGCNbSo39cJSxx2V3RUZK2C1FFTMqygKfC+nPlAuFVPyWK/YyUlUioxvUcVphDu2vCXyT6Rwkke/V0S01tNen3VRK9yfR0ITaU96+GBb8Hx4rmhuf6CTVSZKqbAoVGGmPbwHhhNEI7AsfbxgqTbM+FFVOlOPVEI1aM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715336391; c=relaxed/simple; bh=XquHpfJBGLMPKDC3WMGLV4QXHnt2QU1T4KJjffskmRg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bLhxDh1rNv6991ojT/5IcMqGJ+HmznFTcu/sI/2WLkv2xFmfwb5TjEQ9aDFTPkPHSmZvqzrXTBsXk0vd7OiG+Q5XJawVOnIpzI2HQ0cwvg4gm42j2dtpJByePWlPi94nHGizBQElND16jb07Lm14xg26HF5KZmHftFk+bZddYaY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=rgAfOqvI; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="rgAfOqvI" Received: from [192.168.88.20] (91-158-144-210.elisa-laajakaista.fi [91.158.144.210]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id E4E50289; Fri, 10 May 2024 12:19:42 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1715336383; bh=XquHpfJBGLMPKDC3WMGLV4QXHnt2QU1T4KJjffskmRg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=rgAfOqvIa2cIlLqdpEdAV+UUIz/fIH2/gzisNoQikBdDSp74BqE8eSCoS7pb1332z uNvHlaxQU9QVH3rRWd7Onnu8h9pgJxQ5K01Qj9b1JyXTYdVeb3FDGvCJarV0DhocDZ MAbpW7PYPTOhizEHjpu3A+qHRduDZO6mpolCx/f4= Message-ID: Date: Fri, 10 May 2024 13:19:43 +0300 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 2/2] pmdomain: ti-sci: Support retaining PD boot time state To: Ulf Hansson , Abel Vesa , Saravana Kannan , Stephen Boyd Cc: Nishanth Menon , Tero Kristo , Santosh Shilimkar , Dave Gerlach , J Keerthy , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Santosh Shilimkar , linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org, Devarsh Thakkar References: <20240415-ti-sci-pd-v1-0-a0e56b8ad897@ideasonboard.com> <20240415-ti-sci-pd-v1-2-a0e56b8ad897@ideasonboard.com> From: Tomi Valkeinen Content-Language: en-US Autocrypt: addr=tomi.valkeinen@ideasonboard.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi, On 03/05/2024 16:45, Ulf Hansson wrote: > + Abel, Saravanna, Stephen > > On Mon, 15 Apr 2024 at 19:17, Tomi Valkeinen > wrote: >> >> On 15/04/2024 19:00, Tomi Valkeinen wrote: >>> Add a new flag, TI_SCI_PD_KEEP_BOOT_STATE, which can be set in the dts >>> when referring to power domains. When this flag is set, the ti-sci >>> driver will check if the PD is currently enabled in the HW, and if so, >>> set the GENPD_FLAG_ALWAYS_ON flag so that the PD will stay enabled. >>> >>> The main issue I'm trying to solve here is this: >>> >>> If the Display Subsystem (DSS) has been enabled by the bootloader, the >>> related PD has also been enabled in the HW. When the tidss driver >>> probes, the driver framework will automatically enable the PD. While >>> executing the probe function it is very common for the probe to return >>> EPROBE_DEFER, and, in rarer cases, an actual error. When this happens >>> (probe() returns an error), the driver framework will automatically >>> disable the related PD. >>> >>> Powering off the PD while the DSS is enabled and displaying a picture >>> will cause the DSS HW to enter a bad state, from which (afaik) it can't >>> be woken up except with full power-cycle. Trying to access the DSS in >>> this state (e.g. when retrying the probe) will usually cause the board >>> to hang sooner or later. >>> >>> Even if we wouldn't have this board-hangs issue, it's nice to be able to >>> keep the DSS PD enabled: we want to keep the DSS enabled when the >>> bootloader has enabled the screen. If, instead, we disable the PD at the >>> first EPROBE_DEFER, the screen will (probably) go black. >> >> A few things occurred to me. The driver is supposed to clear the >> GENPD_FLAG_ALWAYS_ON when the driver has probed successfully. There are >> two possible issues with that: >> >> - Afaics, there's no API to do that, and currently I just clear the bit >> in genpd->flags. There's a clear race there, so some locking would be >> required. >> >> - This uses the GENPD_FLAG_ALWAYS_ON flag to say "PD is always on, until >> the driver has started". If the PD would have GENPD_FLAG_ALWAYS_ON set >> for other reasons, the driver would still go and clear the flag, which >> might break things. >> >> Also, unrelated to the above and not a problem in practice at the very >> moment, but I think clocks should also be dealt with somehow. Something, >> at early-ish boot stage, should mark the relevant clocks as in use, so >> that there's no chance they would be turned off when the main kernel has >> started (the main display driver is often a module). >> >> It would be nice to deal with all the above in a single place. I wonder >> if the tidss driver itself could somehow be split into two parts, an >> early part that would probe with minimal dependencies, mainly to reserve >> the core resources without doing any kind of DRM init. And a main part >> which would (somehow) finish the initialization at a later point, when >> we have the filesystem (for firmware) and the other bridge/panel drivers >> have probed. >> >> That can be somewhat achieved with simplefb or simpledrm, though, but we >> can't do any TI DSS specific things there, and it also creates a >> requirement to have either of those drivers built-in, and the related DT >> nodes to be added. > > Without going into too much detail, this and similar problems have > been discussed in the past. With the fw_devlink and the ->sync_state() > callback we are getting closer to a solution, but for genpd a solution > is still pending. > > If you want to read up on earlier discussions and join us moving > forward, that would be great. The last attempt for genpd to move this > forward was posted by Abel Vesa: > https://lore.kernel.org/linux-pm/20230621144019.3219858-1-abel.vesa@linaro.org/ > > Beyond that, we have also discussed various solutions at the last LPC > in Richmond. I think the consensus at that point was that Saravana > targeted to post something for clocks - and when that was done, we > should do the similar thing for genpd. Anyway, I have looped them into > this thread, so they can share any updates on their side of the > matter. If I understand the series correctly, it has an issue at least for this case/platform. The devlinks are between the consumer devices and the PD provider device. TI SCI PD provider has quite a lot of PDs, and all the consumers would have to be probed before any of the PDs could be disabled. So, to get the display PD disabled, I would have to load, e.g., the GPU driver (which I don't even have). I believe this is the case for the clocks also. Perhaps that can be considered a feature, but I fear that in practice it would mean that most of the time for most users all the boot-time enabled powerdomains would be always on. Nevertheless, I believe the series would fix the issue mentioned in this patch, so I'll see if I can get the series working on the TI platform to get a bit more experience on this whole issue. Tomi > >> >> Tomi > > Kind regards > Uffe > >> >>> Another option here would perhaps be to change the driver framework >>> (drivers/base/platform.c) which attaches and detaches the PD, and make >>> it somehow optional, allowing the driver the manage the PD. That option >>> has two downsides: 1) the driver _has_ to manage the PD, which would >>> rule out the use of simplefb and simpledrm, and 2) it would leave the PD >>> in off state from Linux's perspective until a driver enables the PD, and >>> that might mean that the PD gets actually disabled as part of normal >>> system wide power management (disabling unused resources). >>> >>> Yet another option would be to do this outside the ti_sci_pm_domains >>> driver: a piece of code that would somehow be ran after the >>> ti_sci_pm_domains driver has probed (so that we have the PDs), but >>> before tidss/simplefb/simpledrm probes. The problem here is the >>> "somehow" part. Also, this would partly have the same issue 2) as >>> mentioned above. >>> >>> TODO: If this approach is ok, sci-pm-domain.yaml needs to be extended. >>> Also, it sounds a bit like the cell value is not a bit-mask, so maybe >>> adding TI_SCI_PD_KEEP_BOOT_STATE flag this way is not fine. >>> >>> Signed-off-by: Tomi Valkeinen >>> --- >>> drivers/pmdomain/ti/ti_sci_pm_domains.c | 27 +++++++++++++++++++++++++-- >>> include/dt-bindings/soc/ti,sci_pm_domain.h | 1 + >>> 2 files changed, 26 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/pmdomain/ti/ti_sci_pm_domains.c b/drivers/pmdomain/ti/ti_sci_pm_domains.c >>> index 1510d5ddae3d..b71b390aaa39 100644 >>> --- a/drivers/pmdomain/ti/ti_sci_pm_domains.c >>> +++ b/drivers/pmdomain/ti/ti_sci_pm_domains.c >>> @@ -103,7 +103,7 @@ static struct generic_pm_domain *ti_sci_pd_xlate( >>> return ERR_PTR(-ENOENT); >>> >>> genpd_to_ti_sci_pd(genpd_data->domains[idx])->exclusive = >>> - genpdspec->args[1]; >>> + genpdspec->args[1] & TI_SCI_PD_EXCLUSIVE; >>> >>> return genpd_data->domains[idx]; >>> } >>> @@ -161,6 +161,8 @@ static int ti_sci_pm_domain_probe(struct platform_device *pdev) >>> break; >>> >>> if (args.args_count >= 1 && args.np == dev->of_node) { >>> + bool is_on = false; >>> + >>> if (args.args[0] > max_id) { >>> max_id = args.args[0]; >>> } else { >>> @@ -189,7 +191,28 @@ static int ti_sci_pm_domain_probe(struct platform_device *pdev) >>> pd->idx = args.args[0]; >>> pd->parent = pd_provider; >>> >>> - pm_genpd_init(&pd->pd, NULL, true); >>> + /* >>> + * If TI_SCI_PD_KEEP_BOOT_STATE is set and the >>> + * PD has been enabled by the bootloader, set >>> + * the PD to GENPD_FLAG_ALWAYS_ON. This will >>> + * make sure the PD stays enabled until a driver >>> + * takes over and clears the GENPD_FLAG_ALWAYS_ON >>> + * flag. >>> + */ >>> + if (args.args_count > 1 && >>> + args.args[1] & TI_SCI_PD_KEEP_BOOT_STATE) { >>> + /* >>> + * We ignore any error here, and in case >>> + * of error just assume the PD is off. >>> + */ >>> + pd_provider->ti_sci->ops.dev_ops.is_on(pd_provider->ti_sci, >>> + pd->idx, NULL, &is_on); >>> + >>> + if (is_on) >>> + pd->pd.flags |= GENPD_FLAG_ALWAYS_ON; >>> + } >>> + >>> + pm_genpd_init(&pd->pd, NULL, !is_on); >>> >>> list_add(&pd->node, &pd_provider->pd_list); >>> } >>> diff --git a/include/dt-bindings/soc/ti,sci_pm_domain.h b/include/dt-bindings/soc/ti,sci_pm_domain.h >>> index 8f2a7360b65e..af610208e3a3 100644 >>> --- a/include/dt-bindings/soc/ti,sci_pm_domain.h >>> +++ b/include/dt-bindings/soc/ti,sci_pm_domain.h >>> @@ -3,6 +3,7 @@ >>> #ifndef __DT_BINDINGS_TI_SCI_PM_DOMAIN_H >>> #define __DT_BINDINGS_TI_SCI_PM_DOMAIN_H >>> >>> +#define TI_SCI_PD_KEEP_BOOT_STATE 2 >>> #define TI_SCI_PD_EXCLUSIVE 1 >>> #define TI_SCI_PD_SHARED 0 >>> >>> >>