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[98.183.112.25]) by smtp.gmail.com with ESMTPSA id 5614622812f47-3e61035f582sm2271168b6e.47.2024.10.24.08.02.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Oct 2024 08:03:00 -0700 (PDT) Message-ID: <9d801823-aa90-4b15-9dbb-9da6ad2cb3e4@baylibre.com> Date: Thu, 24 Oct 2024 10:02:58 -0500 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 v4 03/15] spi: offload: add support for hardware triggers To: =?UTF-8?Q?Nuno_S=C3=A1?= , Mark Brown , Jonathan Cameron , Rob Herring , Krzysztof Kozlowski , Conor Dooley , =?UTF-8?Q?Nuno_S=C3=A1?= , =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= Cc: Michael Hennerich , Lars-Peter Clausen , David Jander , Martin Sperl , linux-spi@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, linux-pwm@vger.kernel.org References: <20241023-dlech-mainline-spi-engine-offload-2-v4-0-f8125b99f5a1@baylibre.com> <20241023-dlech-mainline-spi-engine-offload-2-v4-3-f8125b99f5a1@baylibre.com> <9762d3f3d3a2e5fbe5e5041cbdc928a9ab24e40b.camel@gmail.com> Content-Language: en-US From: David Lechner In-Reply-To: <9762d3f3d3a2e5fbe5e5041cbdc928a9ab24e40b.camel@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/24/24 9:04 AM, Nuno Sá wrote: > On Wed, 2024-10-23 at 15:59 -0500, David Lechner wrote: >> Extend SPI offloading to support hardware triggers. >> >> This allows an arbitrary hardware trigger to be used to start a SPI >> transfer that was previously set up with spi_optimize_message(). >> >> A new struct spi_offload_trigger is introduced that can be used to >> configure any type of trigger. It has a type discriminator and a union >> to allow it to be extended in the future. Two trigger types are defined >> to start with. One is a trigger that indicates that the SPI peripheral >> is ready to read or write data. The other is a periodic trigger to >> repeat a SPI message at a fixed rate. >> >> There is also a spi_offload_hw_trigger_validate() function that works >> similar to clk_round_rate(). It basically asks the question of if we >> enabled the hardware trigger what would the actual parameters be. This >> can be used to test if the requested trigger type is actually supported >> by the hardware and for periodic triggers, it can be used to find the >> actual rate that the hardware is capable of. >> >> Signed-off-by: David Lechner >> --- >> >> In previous versions, we locked the SPI bus when the hardware trigger >> was enabled, but we found this to be too restrictive. In one use case, >> to avoid a race condition, we need to enable the SPI offload via a >> hardware trigger, then write a SPI message to the peripheral to place >> it into a mode that will generate the trigger. If we did it the other >> way around, we could miss the first trigger. >> >> Another likely use case will be enabling two offloads/triggers at one >> time on the same device, e.g. a read trigger and a write trigger. So >> the exclusive bus lock for a single trigger would be too restrictive in >> this case too. >> >> So for now, I'm going with Nuno's suggestion to leave any locking up to >> the individual controller driver. If we do find we need something more >> generic in the future, we could add a new spi_bus_lock_exclusive() API >> that causes spi_bus_lock() to fail instead of waiting and add "locked" >> versions of trigger enable functions. This would allow a peripheral to >> claim exclusive use of the bus indefinitely while still being able to >> do any SPI messaging that it needs. >> >> v4 changes: >> * Added new struct spi_offload_trigger that is a generic struct for any >>   hardware trigger rather than returning a struct clk. >> * Added new spi_offload_hw_trigger_validate() function. >> * Dropped extra locking since it was too restrictive. >> >> v3 changes: >> * renamed enable/disable functions to spi_offload_hw_trigger_*mode*_... >> * added spi_offload_hw_trigger_get_clk() function >> * fixed missing EXPORT_SYMBOL_GPL >> >> v2 changes: >> * This is split out from "spi: add core support for controllers with >>   offload capabilities". >> * Added locking for offload trigger to claim exclusive use of the SPI >>   bus. >> --- >>  drivers/spi/spi-offload.c       | 266 ++++++++++++++++++++++++++++++++++++++++ >>  include/linux/spi/spi-offload.h |  78 ++++++++++++ >>  2 files changed, 344 insertions(+) >> >> diff --git a/drivers/spi/spi-offload.c b/drivers/spi/spi-offload.c >> index c344cbf50bdb..2a1f9587f27a 100644 >> --- a/drivers/spi/spi-offload.c >> +++ b/drivers/spi/spi-offload.c >> @@ -9,12 +9,26 @@ >>  #include >>  #include >>  #include >> +#include >>  #include >> +#include >>  #include >>  #include >>  #include >>  #include >>   >> +struct spi_offload_trigger { >> + struct list_head list; >> + struct device dev; >> + /* synchronizes calling ops and driver registration */ >> + struct mutex lock; >> + const struct spi_offload_trigger_ops *ops; >> + void *priv; >> +}; >> + >> +static LIST_HEAD(spi_offload_triggers); >> +static DEFINE_MUTEX(spi_offload_triggers_lock); >> + >>  /** >>   * devm_spi_offload_alloc() - Allocate offload instances >>   * @dev: Device for devm purposes >> @@ -102,3 +116,255 @@ struct spi_offload *devm_spi_offload_get(struct device *dev, >>   return offload; >>  } >>  EXPORT_SYMBOL_GPL(devm_spi_offload_get); >> + >> +static void spi_offload_trigger_release(void *data) >> +{ >> + struct spi_offload_trigger *trigger = data; >> + >> + guard(mutex)(&trigger->lock); >> + if (trigger->priv && trigger->ops->release) >> + trigger->ops->release(trigger->priv); >> + >> + put_device(&trigger->dev); >> +} >> + >> +struct spi_offload_trigger >> +*devm_spi_offload_trigger_get(struct device *dev, >> +       struct spi_offload *offload, >> +       enum spi_offload_trigger_type type) >> +{ >> + struct spi_offload_trigger *trigger; >> + struct fwnode_reference_args args; >> + bool match = false; >> + int ret; >> + >> + ret = fwnode_property_get_reference_args(dev_fwnode(offload- >>> provider_dev), >> + "trigger-sources", >> + "#trigger-source-cells", 0, 0, >> + &args); >> + if (ret) >> + return ERR_PTR(ret); >> + >> + struct fwnode_handle *trigger_fwnode __free(fwnode_handle) = args.fwnode; >> + >> + guard(mutex)(&spi_offload_triggers_lock); >> + >> + list_for_each_entry(trigger, &spi_offload_triggers, list) { >> + if (trigger->dev.fwnode != args.fwnode) >> + continue; >> + >> + match = trigger->ops->match(trigger->priv, type, args.args, >> args.nargs); >> + if (match) >> + break; >> + } >> + >> + if (!match) >> + return ERR_PTR(-EPROBE_DEFER); >> + >> + guard(mutex)(&trigger->lock); >> + >> + if (!trigger->priv) >> + return ERR_PTR(-ENODEV); > > This is a bit odd tbh. Not a real deal breaker for me but the typical pattern I would > expect is for methods of the trigger to get a struct spi_offload_trigger opaque > pointer. Then we provide a get_private kind of API for the private data. I guess you > want to avoid that but IMO it makes for neater API instead of getting void pointers. I was just trying to save a step of an extra call to get *priv in each callback implementation, but yeah, no problem to change it to something more "normal" looking. > > Another thing is, can the above actually happen? We have the > spi_offload_triggers_lock grabbed and we got a match so the trigger should not be > able to go away (should block on the same lock). The problem is that it could have gone away before we took the lock. It could happen like this: * Trigger driver registers trigger - sets *priv. * SPI peripheral driver gets reference to trigger. * Trigger driver unregisters trigger - removes *priv. * SPI peripheral tries to call trigger function. > >> >> +struct spi_offload_trigger >> +*devm_spi_offload_trigger_alloc(struct device *dev, >> + struct spi_offload_trigger_info *info) >> +{ >> + struct spi_offload_trigger *trigger; >> + int ret; >> + >> + trigger = kzalloc(sizeof(*trigger), GFP_KERNEL); >> + if (!trigger) >> + return ERR_PTR(-ENOMEM); >> + >> + device_initialize(&trigger->dev); > > Do we really need the full struct device and the overhead of adding it to the driver > core? AFAICT, we're using it only for refcouting so we could use a plain kref for > that matter. It would make things simpler. Or do you envision an future usecase as > this might matter? Like allowing userspace to set some controls on the trigger (I > would expect to be done through consumers though)? Agreed. We should not need a device at this point. > >> + trigger->dev.parent = info->parent; >> + trigger->dev.fwnode = info->fwnode; >> + trigger->dev.of_node = of_node_get(to_of_node(trigger->dev.fwnode)); >> + trigger->dev.of_node_reused = true; >> + trigger->dev.release = spi_offload_trigger_dev_release; >> + >> + mutex_init(&trigger->lock); >> + trigger->ops = info->ops; >> + >> + ret = devm_add_action_or_reset(dev, spi_offload_trigger_put, trigger); >> + if (ret) >> + return ERR_PTR(ret); >> + >> + ret = dev_set_name(&trigger->dev, "%s-%d", info->name, info->id); >> + if (ret) >> + return ERR_PTR(ret); >> + >> + return trigger; >> +} >> +EXPORT_SYMBOL_GPL(devm_spi_offload_trigger_alloc); >> + >> +static void spi_offload_trigger_unregister(void *data) >> +{ >> + struct spi_offload_trigger *trigger = data; >> + >> + scoped_guard(mutex, &spi_offload_triggers_lock) >> + list_del(&trigger->list); >> + >> + guard(mutex)(&trigger->lock); >> + trigger->priv = NULL; > > nit: I guess this is a good as anything else but *ops could also be a good fit to > nullify :) I debated between the two. :-) But if I change the priv handling like you suggest, I think ops will make more sense here.