From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ray Jui Subject: Re: [PATCH v4 2/3] i2c: iproc: Add Broadcom iProc I2C Driver Date: Sat, 17 Jan 2015 12:51:50 -0800 Message-ID: <54BACB66.6040909@broadcom.com> References: <1421274213-3544-1-git-send-email-rjui@broadcom.com> <1421274213-3544-3-git-send-email-rjui@broadcom.com> <20150115084119.GN22880@pengutronix.de> <54B98C18.4080807@broadcom.com> <20150117160113.GA22880@pengutronix.de> <54BABEE9.8070801@broadcom.com> <20150117201849.GC22880@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20150117201849.GC22880-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: =?windows-1252?Q?Uwe_Kleine-K=F6nig?= Cc: Wolfram Sang , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Grant Likely , Christian Daudt , Matt Porter , Florian Fainelli , Russell King , Scott Branden , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, bcm-kernel-feedback-list-dY08KVG/lbpWk0Htik3J/w@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org On 1/17/2015 12:18 PM, Uwe Kleine-K=F6nig wrote: > Hello, >=20 > On Sat, Jan 17, 2015 at 11:58:33AM -0800, Ray Jui wrote: >> On 1/17/2015 8:01 AM, Uwe Kleine-K=F6nig wrote: >>> On Fri, Jan 16, 2015 at 02:09:28PM -0800, Ray Jui wrote: >>>> On 1/15/2015 12:41 AM, Uwe Kleine-K=F6nig wrote: >>>>> On Wed, Jan 14, 2015 at 02:23:32PM -0800, Ray Jui wrote: >>>>>> + */ >>>>>> + val =3D 1 << M_CMD_START_BUSY_SHIFT; >>>>>> + if (msg->flags & I2C_M_RD) { >>>>>> + val |=3D (M_CMD_PROTOCOL_BLK_RD << M_CMD_PROTOCOL_SHIFT) | >>>>>> + (msg->len << M_CMD_RD_CNT_SHIFT); >>>>>> + } else { >>>>>> + val |=3D (M_CMD_PROTOCOL_BLK_WR << M_CMD_PROTOCOL_SHIFT); >>>>>> + } >>>>>> + writel(val, iproc_i2c->base + M_CMD_OFFSET); >>>>>> + >>>>>> + time_left =3D wait_for_completion_timeout(&iproc_i2c->done, ti= me_left); >>>>> >>>>> When the interrupt fires here after the complete timed out and be= fore >>>>> you disable the irq you still throw the result away. >>>> Yes, but then this comes down to the fact that if it has reached t= he >>>> point that is determined to be a timeout condition in the driver, = one >>>> should really treat it as timeout error. In a normal condition, >>>> time_left should never reach zero. >>> I don't agree here. I'm not sure there is a real technical reason, >>> though. But still if you're in a "success after timeout already ove= r" >>> situation it's IMHO better to interpret it as success, not timeout. >>> >> The thing is, the interrupt should never fire after >> wait_for_completion_timeout returns zero here. If it does, then the >> issue is really that the timeout value set in the driver is probably= not >> long enough. I just checked other I2C drivers. I think the way how >> timeout is handled here is consistent with other I2C drivers. > In the presence of Clock stretching there is no (theorethical) upper > limit for the time needed to transfer a given message, is there? So > (theoretically) you can never be sure not to interrupt an ongoing > transfer. >=20 Yes. No theoretical upper limit in the case when clock is stretched by the slave. But how would adding an additional interrupt completion chec= k below help? I assume you want the the check to be like the following? time_left =3D wait_for_completion_timeout(&iproc_i2c->done, time_left)= ; /* disable all interrupts */ writel(0, iproc_i2c->base + IE_OFFSET); if (!time_left && !completion_done()) { dev_err(iproc_i2c->device, "transaction timed out\n"); /* flush FIFOs */ val =3D (1 << M_FIFO_RX_FLUSH_SHIFT) | (1 << M_FIFO_TX_FLUSH_SHIFT); writel(val, iproc_i2c->base + M_FIFO_CTRL_OFFSET); return -ETIMEDOUT; } Does the above code make sense logically? That is, wait_for_completion_timeout has timed out, and we are doing an additional check below to make sure it really has timed out? > And other drivers doing the same is only an excuse to start similar, = but > not to not improve :-) >=20 >>>>>> +static int bcm_iproc_i2c_remove(struct platform_device *pdev) >>>>>> +{ >>>>>> + struct bcm_iproc_i2c_dev *iproc_i2c =3D platform_get_drvdata(p= dev); >>>>>> + >>>>>> + i2c_del_adapter(&iproc_i2c->adapter); >>>>> You need to free the irq before i2c_del_adapter. >>>>> >>>> Yes. Thanks. Change back to use devm_request_irq, and use disable_= irq >>>> here before removing the adapter. >>> The more lightweight approach is to set your device's irq-enable >>> register to zero and call synchronize_irq. (For a shared irq callin= g >>> disable_irq is even wrong here.) >>> >> The fact that IRQF_SHARED flag is not set indicates this is a dedica= ted >> IRQ line, so I thought using disable_irq here makes sense. But if bo= th >> you and Wolfram think masking all I2C interrupts at the block level = + >> synchronize_irq is a better approach, I can change to that. Thanks! > I don't care much. Using synchronize_irq is the more universal approa= ch > and so more likely correct for someone copying from your driver. >=20 Sure, more universal approach and a good example for others. It takes care of both cases of dedicated and shared interrupt. I will make that change. Thanks. > Best regards > Uwe >=20 -- To unsubscribe from this list: send the line "unsubscribe devicetree" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html