linux-kernel - Re: [RESEND v4 1/6] misc: Add Synopsys DesignWare xData IP driver

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Message-ID: <YCLFTjZQ2bCfGC+J@rocinante>
Date:   Tue, 9 Feb 2021 18:24:30 +0100
From:   Krzysztof Wilczyński <kw@...ux.com>
To:     Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>
Cc:     "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Derek Kiernan <derek.kiernan@...inx.com>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [RESEND v4 1/6] misc: Add Synopsys DesignWare xData IP driver

Hi Gustavo,

[...]
> > The code in question would be (exceprt from the patch):
> > 
> > [...]
> > +static int dw_xdata_pcie_probe(struct pci_dev *pdev,
> > +			       const struct pci_device_id *pid)
> > +{
> > +	const struct dw_xdata_pcie_data *pdata = (void *)pid->driver_data;
> > +	struct dw_xdata *dw;
> > [...]
> > +	dw->rg_region.vaddr = pcim_iomap_table(pdev)[pdata->rg_bar];
> > +	if (!dw->rg_region.vaddr)
> > +		return -ENOMEM;
> > [...]
> > 
> > Perhaps something like the following would would?
> > 
> > void __iomem * const *iomap_table;
> > 
> > iomap_table = pcim_iomap_table(pdev);
> > if (!iomap_table)
> >         return -ENOMEM;
> > 
> > dw->rg_region.vaddr = iomap_table[pdata->rg_bar];
> > if (!dw->rg_region.vaddr)
> > 	return -ENOMEM;
> > 
> > With sensible error messages added, of course.  What do you think?
> 
> I think all the improvements are welcome. I will do that.
> My only doubt is if Bjorn recommends removing the 
> iomap_table[pdata->rg_bar] check, after adding the verification on the 
> pcim_iomap_table, because all other drivers doesn't do that.

Good point.  I only found two drivers that do this extra check:

  https://elixir.bootlin.com/linux/v5.11-rc7/source/drivers/crypto/ccp/sp-pci.c#L203
  https://elixir.bootlin.com/linux/v5.11-rc7/source/drivers/net/ethernet/amd/xgbe/xgbe-pci.c#L252

Bjorn, do you think that there is some likelihood that the table might
be missing a mapped address for a given BAR?

I don't think that is the case, but should it be the case, then perhaps
adding a small wrapper that would take a BAR and do all the verification
internally might be a good idea.

Krzysztof