linux-kernel - Re: [PATCH v5 2/6] uio: Add new UIO_MEM_PHYS

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Date:	Wed, 26 Nov 2014 16:01:47 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Ankit Jindal <ankit.jindal@...aro.org>
Cc:	linux-kernel@...r.kernel.org, "Hans J. Koch" <hjk@...sjkoch.de>,
	patches@....com, linux-arm-kernel@...ts.infradead.org,
	Rob Herring <robh+dt@...nel.org>,
	Tushar Jagad <tushar.jagad@...aro.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	devicetree@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
	Varka Bhadram <varkabhadram@...il.com>,
	Kumar Gala <galak@...eaurora.org>,
	Anup Patel <anup@...infault.org>,
	Andreas Färber <afaerber@...e.de>
Subject: Re: [PATCH v5 2/6] uio: Add new UIO_MEM_PHYS_CACHE type for mem
 regions

On Mon, Nov 17, 2014 at 04:06:08PM +0530, Ankit Jindal wrote:
> Currently, three types of mem regions are supported: UIO_MEM_PHYS,
> UIO_MEM_LOGICAL and UIO_MEM_VIRTUAL. Among these UIO_MEM_PHYS helps
> UIO driver export physcial memory to user space as non-cacheable
> user memory. Typcially memory-mapped registers of a device are exported
> to user space as UIO_MEM_PHYS type mem region. The UIO_MEM_PHYS type
> is not efficient if dma-capable devices are capable of maintaining coherency
> with CPU caches.

Not efficient in what way?

> This patch adds new type UIO_MEM_PHYS_CACHE for mem regions to enable
> cacheable access to physical memory from user space.
> 
> Signed-off-by: Ankit Jindal <ankit.jindal@...aro.org>
> Signed-off-by: Tushar Jagad <tushar.jagad@...aro.org>
> ---
>  drivers/uio/uio.c          |   11 ++++++++---
>  include/linux/uio_driver.h |    1 +
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> index 97e6444..120a84b 100644
> --- a/drivers/uio/uio.c
> +++ b/drivers/uio/uio.c
> @@ -644,7 +644,7 @@ static const struct vm_operations_struct uio_physical_vm_ops = {
>  #endif
>  };
>  
> -static int uio_mmap_physical(struct vm_area_struct *vma)
> +static int uio_mmap_physical(struct vm_area_struct *vma, bool cacheable)

I despise "bool" flags in a function, as they don't give any idea of
what is going on when you see the function being called.  Please create
a new function that does this properly, with a correct name, if it's
needed.

thanks,

greg k-h
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