Re: [RFC][PATCH 1/2] uio: allow drivers to override the pgprot for mmap

[Kumar Gala]

On Oct 29, 2011, at 1:38 AM, Greg KH wrote:

 On Fri, Oct 28, 2011 at 11:48:12PM +0200, Hans J. Koch wrote:
 On Fri, Oct 28, 2011 at 10:50:29AM -0500, Kumar Gala wrote:
 For some devices, the default behavior of pgprot_noncached() is not
 appropriate for all of its mappable regions. This provides a means for
 the kernel side of the UIO driver to override the flags without having
 to implement its own full mmap callback.
 
 Thanks for also providing an example driver showing the use of this.
 You should also post this driver in a mainline-ready version, I'm a bit
 uncomfortable with adding a new function pointer without having any users.
 
 I'm more than uncomfortable, I'll refuse to take any such patch unless
 there is a in-kernel user, otherwise it makes no sense to add the
 pointer at all.
 
 thanks,
 
 greg k-h

I'm in agreement with this view.  I wanted to post this to make sure the 
direction we took was ok so when the upstream driver is posted this patch / 
change isn't a concern.

- k
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Re: [RFC][PATCH 1/2] uio: allow drivers to override the pgprot for mmap

[Greg KH]

On Fri, Oct 28, 2011 at 11:48:12PM +0200, Hans J. Koch wrote:
 On Fri, Oct 28, 2011 at 10:50:29AM -0500, Kumar Gala wrote:
  For some devices, the default behavior of pgprot_noncached() is not
  appropriate for all of its mappable regions. This provides a means for
  the kernel side of the UIO driver to override the flags without having
  to implement its own full mmap callback.
 
 Thanks for also providing an example driver showing the use of this.
 You should also post this driver in a mainline-ready version, I'm a bit
 uncomfortable with adding a new function pointer without having any users.

I'm more than uncomfortable, I'll refuse to take any such patch unless
there is a in-kernel user, otherwise it makes no sense to add the
pointer at all.

thanks,

greg k-h
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Re: [RFC][PATCH 1/2] uio: allow drivers to override the pgprot for mmap

[Hans J. Koch]

On Fri, Oct 28, 2011 at 10:50:29AM -0500, Kumar Gala wrote:
 For some devices, the default behavior of pgprot_noncached() is not
 appropriate for all of its mappable regions. This provides a means for
 the kernel side of the UIO driver to override the flags without having
 to implement its own full mmap callback.

Thanks for also providing an example driver showing the use of this.
You should also post this driver in a mainline-ready version, I'm a bit
uncomfortable with adding a new function pointer without having any users.

And since you change uio_driver.h you should also update documentation
accordingly (Documentation/DocBook/uio-howto.tmpl).

Otherwise, I have no general objections.

Thanks,
Hans

 
 Signed-off-by: Kumar Gala ga...@kernel.crashing.org
 Signed-off-by: Geoff Thorpe ge...@geoffthorpe.net
 ---
  drivers/uio/uio.c  |6 +-
  include/linux/uio_driver.h |3 +++
  2 files changed, 8 insertions(+), 1 deletions(-)
 
 diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
 index dc27d89..0aebe27 100644
 --- a/drivers/uio/uio.c
 +++ b/drivers/uio/uio.c
 @@ -655,7 +655,11 @@ static int uio_mmap_physical(struct vm_area_struct *vma)
  
   vma-vm_flags |= VM_IO | VM_RESERVED;
  
 - vma-vm_page_prot = pgprot_noncached(vma-vm_page_prot);
 + if (idev-info-set_pgprot)
 + vma-vm_page_prot = idev-info-set_pgprot(idev-info, mi,
 +vma-vm_page_prot);
 + else
 + vma-vm_page_prot = pgprot_noncached(vma-vm_page_prot);
  
   return remap_pfn_range(vma,
  vma-vm_start,
 diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
 index fd99ff9..edfe7c8 100644
 --- a/include/linux/uio_driver.h
 +++ b/include/linux/uio_driver.h
 @@ -80,6 +80,7 @@ struct uio_device;
   * @open:open operation for this uio device
   * @release: release operation for this uio device
   * @irqcontrol:  disable/enable irqs when 0/1 is written to 
 /dev/uioX
 + * @set_pgprot:  allow driver to override default(noncached) 
 pgprot
   */
  struct uio_info {
   struct uio_device   *uio_dev;
 @@ -95,6 +96,8 @@ struct uio_info {
   int (*open)(struct uio_info *info, struct inode *inode);
   int (*release)(struct uio_info *info, struct inode *inode);
   int (*irqcontrol)(struct uio_info *info, s32 irq_on);
 + pgprot_t (*set_pgprot)(struct uio_info *uio, unsigned int mem_idx,
 +pgprot_t prot);
  };
  
  extern int __must_check
 -- 
 1.7.3.4
 
 
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