linux-kernel - Re: [PATCH v3 10/25] bus: mhi: ep: Add support for creating and destroying MHI EP devices

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Date:   Thu, 17 Feb 2022 17:34:39 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Alex Elder <elder@...aro.org>
Cc:     mhi@...ts.linux.dev, quic_hemantk@...cinc.com,
        quic_bbhatt@...cinc.com, quic_jhugo@...cinc.com,
        vinod.koul@...aro.org, bjorn.andersson@...aro.org,
        dmitry.baryshkov@...aro.org, quic_vbadigan@...cinc.com,
        quic_cang@...cinc.com, quic_skananth@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/25] bus: mhi: ep: Add support for creating and
 destroying MHI EP devices

On Tue, Feb 15, 2022 at 02:02:57PM -0600, Alex Elder wrote:

[...]

> > +
> > +	mhi_dev = mhi_ep_alloc_device(mhi_cntrl, MHI_DEVICE_XFER);
> > +	if (IS_ERR(mhi_dev))
> > +		return PTR_ERR(mhi_dev);
> 
> It looks like the only possible error is no memory, so you could
> just have mhi_ep_alloc_device() return NULL.
> 

I think returning the actual error is more safe as we may end up adding more
stuff into this function in the future.

> > +
> > +	/* Configure primary channel */
> > +	mhi_dev->ul_chan = mhi_chan;
> > +	get_device(&mhi_dev->dev);
> > +	mhi_chan->mhi_dev = mhi_dev;
> > +
> > +	/* Configure secondary channel as well */
> > +	mhi_chan++;
> > +	mhi_dev->dl_chan = mhi_chan;
> > +	get_device(&mhi_dev->dev);
> > +	mhi_chan->mhi_dev = mhi_dev;
> > +
> > +	/* Channel name is same for both UL and DL */
> > +	mhi_dev->name = mhi_chan->name;
> > +	dev_set_name(&mhi_dev->dev, "%s_%s",
> > +		     dev_name(&mhi_cntrl->mhi_dev->dev),
> > +		     mhi_dev->name);
> > +
> > +	ret = device_add(&mhi_dev->dev);
> > +	if (ret)
> > +		put_device(&mhi_dev->dev);
> > +
> > +	return ret;
> > +}
> > +
> > +static int mhi_ep_destroy_device(struct device *dev, void *data)
> > +{
> > +	struct mhi_ep_device *mhi_dev;
> > +	struct mhi_ep_cntrl *mhi_cntrl;
> > +	struct mhi_ep_chan *ul_chan, *dl_chan;
> > +
> > +	if (dev->bus != &mhi_ep_bus_type)
> > +		return 0;
> > +
> > +	mhi_dev = to_mhi_ep_device(dev);
> > +	mhi_cntrl = mhi_dev->mhi_cntrl;
> > +
> > +	/* Only destroy devices created for channels */
> > +	if (mhi_dev->dev_type == MHI_DEVICE_CONTROLLER)
> > +		return 0;
> > +
> > +	ul_chan = mhi_dev->ul_chan;
> > +	dl_chan = mhi_dev->dl_chan;
> 
> Aren't they required to supply *both* channels?  Or maybe
> it's just required that there are transfer callback functions
> for both channels.  Anyway, no need to check for null, because
> the creation function guarantees they're both non-null I think.
> 

mhi_ep_destroy_device() will be called for each device separately. So we
must check for NULL.

Thanks,
Mani