linux-kernel - Re: [PATCH] auxdisplay/cfag12864bfb.c: Replace vm_insert

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Message-ID: <CANiq72kQA45ekbSruh-zTsc9B-9EOxZna=cOgOcM7--owxrWsA@mail.gmail.com>
Date:   Thu, 20 Sep 2018 23:26:16 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     willy@...radead.org, linux-kernel <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] auxdisplay/cfag12864bfb.c: Replace vm_insert_page

On Thu, Sep 20, 2018 at 10:23 PM, Souptick Joarder <jrdr.linux@...il.com> wrote:
> There is a plan to remove vm_insert_page permanently
> and replace it with new API vmf_insert_page which will
> return vm_fault_t type. As part of it vm_insert_page
> is removed from this driver.

A link to the discussion/plan would be nice. The commit 1c8f422059ae5
("mm: change return type to vm_fault_t") explains a bit, but has a
broken link :( Googling for the stuff returns many of the patches, but
not the actual discussion...

>  static int cfag12864bfb_mmap(struct fb_info *info, struct vm_area_struct *vma)
>  {
> -       return vm_insert_page(vma, vma->vm_start,
> -               virt_to_page(cfag12864b_buffer));
> +       struct page *page;
> +       unsigned long size = vma->vm_end - vma->vm_start;
> +
> +       page = virt_to_page(cfag12864b_buffer);
> +       return remap_pfn_range(vma, vma->vm_start, page_to_pfn(page),
> +                               size, vma->vm_page_prot);

I am out of the loop on these mm changes, so please indulge me, but:

  * Why is there no documentation on vmf_insert_page() while
vm_insert_page() had it? (specially since it seems you want to remove
vm_insert_page()).

  * Shouldn't we have a simple remap_page() or remap_kernel_page() to
fit this use case and avoid that dance? (another driver in auxdisplay
will require the same change, and I guess others in the kernel as
well).

Thanks!

Cheers,
Miguel