linux-kernel - Re: [PATCH v2 1/4] ACPI / watchdog: Add support for WDAT hardware watchdog

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Date:   Tue, 20 Sep 2016 16:50:07 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Wim Van Sebroeck <wim@...ana.be>,
        Len Brown <lenb@...nel.org>, Jean Delvare <jdelvare@...e.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Peter Tyser <ptyser@...-inc.com>,
        Lee Jones <lee.jones@...aro.org>,
        Zha Qipeng <qipeng.zha@...el.com>,
        Darren Hart <dvhart@...radead.org>, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] ACPI / watchdog: Add support for WDAT hardware
 watchdog

On Tue, Sep 20, 2016 at 06:37:23AM -0700, Guenter Roeck wrote:
> > +	for (i = 0; i < tbl->entries; i++) {
> > +		const struct acpi_generic_address *gas;
> > +		struct wdat_instruction *instr;
> > +		struct list_head *instructions;
> > +		unsigned int action;
> > +		struct resource r;
> > +		int j;
> > +
> > +		action = entries[i].action;
> > +		if (action >= MAX_WDAT_ACTIONS) {
> > +			dev_dbg(&pdev->dev, "Skipping unknown action: %u\n",
> > +				action);
> > +			continue;
> > +		}
> > +
> > +		instr = devm_kzalloc(&pdev->dev, sizeof(*instr), GFP_KERNEL);
> > +		if (!instr)
> > +			return -ENOMEM;
> > +
> > +		INIT_LIST_HEAD(&instr->node);
> > +		instr->entry = entries[i];
> > +
> > +		gas = &entries[i].register_region;
> > +
> > +		memset(&r, 0, sizeof(r));
> > +		r.start = gas->address;
> > +		r.end = r.start + gas->access_width;
> > +		if (gas->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> > +			r.flags = IORESOURCE_MEM;
> > +		} else if (gas->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
> > +			r.flags = IORESOURCE_IO;
> > +		} else {
> > +			dev_dbg(&pdev->dev, "Unsupported address space: %d\n",
> > +				gas->space_id);
> > +			continue;
> > +		}
> > +
> > +		/* Find the matching resource */
> > +		for (j = 0; j < pdev->num_resources; j++) {
> > +			res = &pdev->resource[j];
> > +			if (resource_contains(res, &r)) {
> > +				instr->reg = regs[j] + r.start - res->start;
> > +				break;
> > +			}
> > +		}
> > +
> > +		if (!instr->reg) {
> > +			dev_err(&pdev->dev, "I/O resource not found\n");
> > +			return -EINVAL;
> > +		}
> > +
> I must be missing something here. What is happening with instr ?

Instr contains the actual instruction from WDAT table. There can be
many.

> > +		instructions = wdat->instructions[action];

This will be NULL first time so...

> > +		if (!instructions) {
> > +			instructions = devm_kzalloc(&pdev->dev,
> > +					sizeof(*instructions), GFP_KERNEL);
> > +			if (!instructions)
> > +				return -ENOMEM;
> > +
> > +			INIT_LIST_HEAD(instructions);
> > +			wdat->instructions[action] = instructions;
> 
> ... and I don't really see how wdat->instructions[action] contains anything but
> a zero filled array. Confused :-(.

...we allocate entry for that here. Next time it will not be NULL for
that action.

> 
> > +		}
> > +
> > +		list_add_tail(&instr->node, instructions);

Then we append each instr to the list for this action.

Hope this clarifies :)