linux-kernel - Re: [PATCH v4 05/11] VAS: Define helpers for access MMIO regions

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Date:   Mon, 24 Apr 2017 16:28:07 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     michael.neuling@....ibm.com, stewart@...ux.vnet.ibm.com,
        apopple@....ibm.com, hbabu@...ibm.com, oohall@...il.com,
        bsingharora@...il.com, linuxppc-dev@...abs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 05/11] VAS: Define helpers for access MMIO regions

On Thu, 2017-03-30 at 22:13 -0700, Sukadev Bhattiprolu wrote:
> +static void *map_mmio_region(char *name, uint64_t start, int len)
> +{
> +       void *map;
> +
> +       if (!request_mem_region(start, len, name)) {
> +               pr_devel("%s(): request_mem_region(0x%llx, %d) failed\n",
> +                               __func__, start, len);
> +               return NULL;
> +       }
> +
> +       map = __ioremap(start, len, pgprot_val(pgprot_cached(__pgprot(0))));
> +       if (!map) {
> +               pr_devel("%s(): ioremap(0x%llx, %d) failed\n", __func__, start,
> +                               len);
> +               return NULL;
> +       }
> +
> +       return map;
> +}

That's very wrong. I assume this never worked right ?

MMIO regions must be mapped non-cachable. Only the paste region
requires being mapped cachable. Ask Aneesh for a cleaner way of
doing it too while at it.

> +/*
> + * Unmap the MMIO regions for a window.
> + */
> +static void unmap_wc_paste_kaddr(struct vas_window *window)
> +{
> +       int len;

Don't use "wc"... that usually means "write combine".

Cheers,
Ben.