linux-kernel - Re: [PATCH v2 1/3] media: V3s: Add support for Allwinner CSI.

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Message-ID: <20170823192413.y5psmcgd3ghvpkbz@flea.home>
Date:   Wed, 23 Aug 2017 21:24:13 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Yong <yong.deng@...ewell.com>
Cc:     Baruch Siach <baruch@...s.co.il>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Hans Verkuil <hverkuil@...all.nl>,
        Arnd Bergmann <arnd@...db.de>,
        Hugues Fruchet <hugues.fruchet@...com>,
        Yannick Fertre <yannick.fertre@...com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Benoit Parrot <bparrot@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Jean-Christophe Trotin <jean-christophe.trotin@...com>,
        Ramesh Shanmugasundaram <ramesh.shanmugasundaram@...renesas.com>,
        Minghsiu Tsai <minghsiu.tsai@...iatek.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v2 1/3] media: V3s: Add support for Allwinner CSI.

On Wed, Aug 23, 2017 at 10:41:18AM +0800, Yong wrote:
> > > > > +static irqreturn_t sun6i_csi_isr(int irq, void *dev_id)
> > > > > +{
> > > > > +	struct sun6i_csi_dev *sdev = (struct sun6i_csi_dev *)dev_id;
> > > > > +	struct regmap *regmap = sdev->regmap;
> > > > > +	u32 status;
> > > > > +
> > > > > +	regmap_read(regmap, CSI_CH_INT_STA_REG, &status);
> > > > > +
> > > > > +	if ((status & CSI_CH_INT_STA_FIFO0_OF_PD) ||
> > > > > +	    (status & CSI_CH_INT_STA_FIFO1_OF_PD) ||
> > > > > +	    (status & CSI_CH_INT_STA_FIFO2_OF_PD) ||
> > > > > +	    (status & CSI_CH_INT_STA_HB_OF_PD)) {
> > > > > +		regmap_write(regmap, CSI_CH_INT_STA_REG, status);
> > > > > +		regmap_update_bits(regmap, CSI_EN_REG, CSI_EN_CSI_EN, 0);
> > > > > +		regmap_update_bits(regmap, CSI_EN_REG, CSI_EN_CSI_EN,
> > > > > +				   CSI_EN_CSI_EN);
> > > > 
> > > > You need to enable / disable it at every frame? How do you deal with
> > > > double buffering? (or did you choose to ignore it for now?)
> > > 
> > > These *_OF_PD status bits indicate an overflow error condition.
> > 
> > Shouldn't we return an error code then? The names of these flags could
> > be better too.
> 
> Then, where and how to deal with the error coce.

If you want to deal with FIFO overflow, I'm not sure you have anything
to do. It means, you've been to slow to queue buffers, so I guess
stopping the pipeline until more buffers are queued would make
sense. And we should probably increase the sequence number while doing
so to notify the userspace that some frames were lost.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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