linux-kernel - Re: [PATCH RFC 1/3] tpm_crb: expand struct crb_control_area to struct crb

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Date:   Sun, 9 Oct 2016 10:49:05 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        "moderated list:TPM DEVICE DRIVER" 
        <tpmdd-devel@...ts.sourceforge.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 1/3] tpm_crb: expand struct crb_control_area to
 struct crb_regs

On Sun, Oct 09, 2016 at 12:38:18PM +0300, Jarkko Sakkinen wrote:
> On Sat, Oct 08, 2016 at 07:42:56PM -0600, Jason Gunthorpe wrote:
> > On Sun, Oct 09, 2016 at 03:15:09AM +0300, Jarkko Sakkinen wrote:
> > > +	ctrl = crb_map_res(dev, priv, &io_res, buf->control_address,
> > > +			   sizeof(struct crb_regs) -
> > > +			   offsetof(struct crb_regs, ctrl_req));
> > > +	if (IS_ERR(ctrl))
> > > +		return PTR_ERR(ctrl);
> > > +
> > > +	/* The control area always overrlaps IO memory mapped from the ACPI
> > > +	 * object with CRB start only devices. Thus, this is perfectly safe.
> > > +	 */
> > > +	priv->regs = (void *)((unsigned long)ctrl -
> > > +		offsetof(struct crb_regs, ctrl_req));
> > 
> > Hum. No, this makes bad assumptions about the structure of iomapping.
> > 
> > The map itself needs to be done with the adjustment:
> > 
> > 	ctrl = crb_map_res(dev, priv, &io_res, buf->control_address -
> > 		offsetof(struct crb_regs, ctrl_req),
> > 	   	sizeof(struct crb_regs));
> 
> That would be wrong address for the control area as it does not start
> from the beginning of CRB registers.

Of course, I just pointed out what the map call should look like

Something like this

 	priv->regs = crb_map_res(dev, priv, &io_res, buf->control_address -
 		offsetof(struct crb_regs, ctrl_req),
 	   	sizeof(struct crb_regs));
        ctrl = &priv->regs.ctrl_req;

> I think the crb_map_io and crb_map_res are too generic. Better way to do
> things would be to validate that assumptions for these two cases hold.

If the driver is going to be using a negative offset like this, then
it very much should validate the assumptions before doing it.

and not even map these regsiters if they are not supported by
hardware.

Jason