From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?Q?Andreas_F=c3=a4rber?= Subject: Re: [PATCH v3 lora-next 5/5] net: lora: sx125x sx1301: allow radio to register as a clk provider Date: Mon, 31 Dec 2018 23:56:40 +0100 Message-ID: References: <1539361567-3602-1-git-send-email-ben.whitten@lairdtech.com> <1539361567-3602-6-git-send-email-ben.whitten@lairdtech.com> <491d1a46-c112-1106-9f25-14149f0dcbd0@suse.de> <20181231175034.GI1846@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20181231175034.GI1846@sirena.org.uk> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Mark Brown Cc: Ben Whitten , devicetree , "David S. Miller" , netdev@vger.kernel.org, Michael Turquette , Stephen Boyd , "linux-lpwan@lists.infradead.org" , linux-kernel@vger.kernel.org, starnight@g.ncu.edu.tw, linux-clk , "linux-spi@vger.kernel.org" , Maxime Ripard , "linux-arm-kernel@lists.infradead.org" , Russell King List-Id: devicetree@vger.kernel.org Am 31.12.18 um 18:50 schrieb Mark Brown: > On Sun, Dec 30, 2018 at 11:55:46AM +0100, Andreas Färber wrote: >> Given that observed symptoms were CPU stalls, workqueue hangs and RCU >> problems, requiring a power-cycle to recover, I wonder whether we are >> running into some atomic/locking issue with clk_enable()? Is it valid at >> all to use SPI/regmap for clk_enable()? If it is, is there a known issue >> specific to spi-sun6i (A64) in 4.20.0? >> I already tried setting .disable_locking = true in both regmap_configs. >> Any suggestions how to further debug? > > You can't use SPI for clk_enable(), clk_enable() needs to be doable in > atomic context since we need to wait for the bus operations to complete > (you can start SPI transfers in atomic context but you still need to > wait for them to complete). Any clocks that are only accessible via a > slow bus like I2C or SPI need to do the enable/disable in the > prepare/unprepare operations which aren't done in atomic context. > > regmap can be used in atomic contexts, though you need to configure it > to use spinlocks instead of mutexes and ensure that no register cache > allocations happen during I/O (eg, by providing defaults for all > registers or by not using a cache). We have .cache_type = REGCACHE_NONE on both bus and spi regmap_configs. I moved the regmap_field_write() from .enable to .prepare and set .fast_io = true on both regmap_configs to force using spinlocks, but same hang as in .enable before... And same if I set .disable_locking = true on both. Given that it works with one SPI driver and not with the other, independent of the locking options applied, I assume my symptoms are not a regmap-layer issue. Is it allowed during a .prepare operation to call the mentioned clk_get_rate(), which ends up calling clk_prepare_lock()? According to my debug output in spi-sun6i.c our hanging regmap_field_write() ends up calling sun6i_transfer_one() three times, the first two look okay, but the third one doesn't make it past the clk_get_rate() or following if block. [But for now some fireworks...] Regards, Andreas -- SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg)