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

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Date:   Tue, 15 Feb 2022 14:02:57 -0600
From:   Alex Elder <elder@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        mhi@...ts.linux.dev
Cc:     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 2/12/22 12:21 PM, Manivannan Sadhasivam wrote:
> This commit adds support for creating and destroying MHI endpoint devices.
> The MHI endpoint devices binds to the MHI endpoint channels and are used
> to transfer data between MHI host and endpoint device.
> 
> There is a single MHI EP device for each channel pair. The devices will be
> created when the corresponding channels has been started by the host and
> will be destroyed during MHI EP power down and reset.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

A few comments again, nothing major.

					-Alex

> ---
>   drivers/bus/mhi/ep/main.c | 77 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 77 insertions(+)
> 
> diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
> index f66404181972..fcaacf9ddbd1 100644
> --- a/drivers/bus/mhi/ep/main.c
> +++ b/drivers/bus/mhi/ep/main.c
> @@ -67,6 +67,83 @@ static struct mhi_ep_device *mhi_ep_alloc_device(struct mhi_ep_cntrl *mhi_cntrl,
>   	return mhi_dev;
>   }
>   
> +/*
> + * MHI channels are always defined in pairs with UL as the even numbered
> + * channel and DL as odd numbered one.
> + */

Awesome comment.  And it seems that the channel ID passed
here is even, and that there *must* be a second mhi_chan[]
entry after the one specified.  And UL is also called the
"primary" channel.

> +static int mhi_ep_create_device(struct mhi_ep_cntrl *mhi_cntrl, u32 ch_id)
> +{
> +	struct mhi_ep_chan *mhi_chan = &mhi_cntrl->mhi_chan[ch_id];
> +	struct mhi_ep_device *mhi_dev;
> +	int ret;
> +
> +	/* Check if the channel name is same for both UL and DL */
> +	if (strcmp(mhi_chan->name, mhi_chan[1].name))
> +		return -EINVAL;

Maybe log an error to say what's wrong with it?

> +
> +	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.

> +
> +	/* 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.

> +	if (ul_chan)
> +		put_device(&ul_chan->mhi_dev->dev);
> +
> +	if (dl_chan)
> +		put_device(&dl_chan->mhi_dev->dev);
> +
> +	dev_dbg(&mhi_cntrl->mhi_dev->dev, "Destroying device for chan:%s\n",
> +		 mhi_dev->name);
> +
> +	/* Notify the client and remove the device from MHI bus */
> +	device_del(dev);
> +	put_device(dev);
> +
> +	return 0;
> +}
> +
>   static int parse_ch_cfg(struct mhi_ep_cntrl *mhi_cntrl,
>   			const struct mhi_ep_cntrl_config *config)
>   {