linux-kernel - Re: [PATCH 1/4] PCI: add resizeable BAR infrastructure v4

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Message-ID: <CAHp75VfJKkFTXbia=CiZapriEg6ObUh=js6cKJv3xe=2DBHbqA@mail.gmail.com>
Date:   Wed, 26 Apr 2017 19:45:30 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Christian König <deathsimple@...afone.de>
Cc:     helgaas@...nel.org,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] PCI: add resizeable BAR infrastructure v4

On Tue, Apr 25, 2017 at 4:19 PM, Christian König
<deathsimple@...afone.de> wrote:
> From: Christian König <christian.koenig@....com>
>
> Just the defines and helper functions to read the possible sizes of a BAR and
> update it's size.
>
> See https://pcisig.com/sites/default/files/specification_documents/ECN_Resizable-BAR_24Apr2008.pdf
> and PCIe r3.1, sec 7.22.
>
> This is useful for hardware with large local storage (mostly GFX) which only
> expose 256MB BARs initially to be compatible with 32bit systems.

> +u32 pci_rbar_get_possible_sizes(struct pci_dev *pdev, int bar)
> +{

> +       unsigned pos, nbars;
> +       u32 ctrl, cap;
> +       unsigned i;

Are we supposed to use plain 'unsigned' nowadays? I would go with
'unsigned int'.

> +}

> + * Returns size if found or negativ error code.

Typo: negative.

> +int pci_rbar_get_current_size(struct pci_dev *pdev, int bar)
> +{
> +       unsigned pos, nbars;

> +       u32 ctrl;
> +       unsigned i;

Reversed tree order?

> +       for (i = 0; i < nbars; ++i, pos += 8) {
> +               int bar_idx;
> +
> +               pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
> +               bar_idx = (ctrl & PCI_REBAR_CTRL_BAR_IDX_MASK) >>
> +                               PCI_REBAR_CTRL_BAR_IDX_SHIFT;
> +               if (bar_idx != bar)
> +                       continue;
> +
> +               return (ctrl & PCI_REBAR_CTRL_BAR_SIZE_MASK) >>
> +                       PCI_REBAR_CTRL_BAR_SIZE_SHIFT;
> +       }

This one the same as previous function, the difference only in what is
returned. CAre to split static helper function for both?

> +       return -ENOENT;
> +}

> +/**
> + * pci_rbar_set_size - set a new size for a BAR
> + * @dev: PCI device
> + * @bar: BAR to set size to

> + * @size: new size as defined in the spec (log2(size in bytes) - 20)

Not clear is it rounded up / down. I would go with "...in the spec
(0=1MB, 19=512GB)".

> + *
> + * Set the new size of a BAR as defined in the spec (0=1MB, 19=512GB).
> + * Returns true if resizing was successful, false otherwise.
> + */

> +int pci_rbar_set_size(struct pci_dev *pdev, int bar, int size)
> +{
> +       unsigned pos, nbars;
> +       u32 ctrl;
> +       unsigned i;


> +
> +       pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_REBAR);
> +       if (!pos)
> +               return -ENOTSUPP;
> +
> +       pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
> +       nbars = (ctrl & PCI_REBAR_CTRL_NBAR_MASK) >> PCI_REBAR_CTRL_NBAR_SHIFT;
> +
> +       for (i = 0; i < nbars; ++i, pos += 8) {
> +               int bar_idx;
> +
> +               pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
> +               bar_idx = (ctrl & PCI_REBAR_CTRL_BAR_IDX_MASK) >>
> +                               PCI_REBAR_CTRL_BAR_IDX_SHIFT;
> +               if (bar_idx != bar)
> +                       continue;

Above is duplicating previous.

So,
static int ..._find_rbar(..., u32 *ctrl)
{
}

Returns: (i.e.) 0 - found, 1 - not found, -ERRNO.

ret = _find_rbar();
if (ret < 0)
 return ret;
if (ret)
 return -ENOENT;
...
return 0;

So, please refactor.

> +
> +               ctrl &= ~PCI_REBAR_CTRL_BAR_SIZE_MASK;
> +               ctrl |= size << PCI_REBAR_CTRL_BAR_SIZE_SHIFT;
> +               pci_write_config_dword(pdev, pos + PCI_REBAR_CTRL, ctrl);
> +               return 0;
> +       }
> +
> +       return -ENOENT;
> +}

> -#define  PCI_REBAR_CTRL_NBAR_MASK      (7 << 5)        /* mask for # bars */
> -#define  PCI_REBAR_CTRL_NBAR_SHIFT     5       /* shift for # bars */

> +#define  PCI_REBAR_CTRL_NBAR_MASK      (7 << 5)        /* mask for # BARs */
> +#define  PCI_REBAR_CTRL_NBAR_SHIFT     5       /* shift for # BARs */

I understand why, but I dunno it worth to do.

-- 
With Best Regards,
Andy Shevchenko