linux-kernel - Re: [PATCH] Add memory mapped RTC driver for UV

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Message-ID: <28c262360909102301v5d1c32b9lb3290a6a31f49d17@mail.gmail.com>
Date:	Fri, 11 Sep 2009 15:01:16 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dimitri Sivanich <sivanich@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Hugh Dickins <hugh.dickins@...cali.co.uk>
Subject: Re: [PATCH] Add memory mapped RTC driver for UV

On Fri, Sep 11, 2009 at 2:52 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Thu, 10 Sep 2009 20:30:54 -0500 Dimitri Sivanich <sivanich@....com> wrote:
>
>> This driver memory maps the UV Hub RTC.
>>
>> ...
>>
>> +/**
>> + * uv_mmtimer_ioctl - ioctl interface for /dev/uv_mmtimer
>> + * @file: file structure for the device
>> + * @cmd: command to execute
>> + * @arg: optional argument to command
>> + *
>> + * Executes the command specified by @cmd.  Returns 0 for success, < 0 for
>> + * failure.
>> + *
>> + * Valid commands:
>> + *
>> + * %MMTIMER_GETOFFSET - Should return the offset (relative to the start
>> + * of the page where the registers are mapped) for the counter in question.
>> + *
>> + * %MMTIMER_GETRES - Returns the resolution of the clock in femto (10^-15)
>> + * seconds
>> + *
>> + * %MMTIMER_GETFREQ - Copies the frequency of the clock in Hz to the address
>> + * specified by @arg
>> + *
>> + * %MMTIMER_GETBITS - Returns the number of bits in the clock's counter
>> + *
>> + * %MMTIMER_MMAPAVAIL - Returns 1 if registers can be mmap'd into userspace
>> + *
>> + * %MMTIMER_GETCOUNTER - Gets the current value in the counter and places it
>> + * in the address specified by @arg.
>
> Are these % thingies part of kerneldoc?
>
>> + */
>> +static long uv_mmtimer_ioctl(struct file *file, unsigned int cmd,
>> +                                             unsigned long arg)
>> +{
>> +     int ret = 0;
>> +
>> +     switch (cmd) {
>> +     case MMTIMER_GETOFFSET: /* offset of the counter */
>> +             /*
>> +              * UV RTC register is on it's own page
>
> "its" ;)
>
>> +              */
>> +             if (PAGE_SIZE <= (1 << 16))
>> +                     ret = ((UV_LOCAL_MMR_BASE | UVH_RTC) & (PAGE_SIZE-1))
>> +                             / 8;
>> +             else
>> +                     ret = -ENOSYS;
>> +             break;
>> +
>> +     case MMTIMER_GETRES: /* resolution of the clock in 10^-15 s */
>> +             if (copy_to_user((unsigned long __user *)arg,
>> +                             &uv_mmtimer_femtoperiod, sizeof(unsigned long)))
>> +                     ret = -EFAULT;
>> +             break;
>> +
>> +     case MMTIMER_GETFREQ: /* frequency in Hz */
>> +             if (copy_to_user((unsigned long __user *)arg,
>> +                             &sn_rtc_cycles_per_second,
>> +                             sizeof(unsigned long)))
>> +                     ret = -EFAULT;
>> +             break;
>> +
>> +     case MMTIMER_GETBITS: /* number of bits in the clock */
>> +             ret = hweight64(UVH_RTC_REAL_TIME_CLOCK_MASK);
>> +             break;
>> +
>> +     case MMTIMER_MMAPAVAIL: /* can we mmap the clock into userspace? */
>> +             ret = (PAGE_SIZE <= (1 << 16)) ? 1 : 0;
>> +             break;
>> +
>> +     case MMTIMER_GETCOUNTER:
>> +             if (copy_to_user((unsigned long __user *)arg,
>> +                             (unsigned long *)uv_local_mmr_address(UVH_RTC),
>> +                             sizeof(unsigned long)))
>> +                     ret = -EFAULT;
>> +             break;
>> +     default:
>> +             ret = -ENOTTY;
>> +             break;
>> +     }
>> +     return ret;
>> +}
>> +
>> +/**
>> + * uv_mmtimer_mmap - maps the clock's registers into userspace
>> + * @file: file structure for the device
>> + * @vma: VMA to map the registers into
>> + *
>> + * Calls remap_pfn_range() to map the clock's registers into
>> + * the calling process' address space.
>> + */
>> +static int uv_mmtimer_mmap(struct file *file, struct vm_area_struct *vma)
>> +{
>> +     unsigned long uv_mmtimer_addr;
>> +
>> +     if (vma->vm_end - vma->vm_start != PAGE_SIZE)
>> +             return -EINVAL;
>> +
>> +     if (vma->vm_flags & VM_WRITE)
>> +             return -EPERM;
>> +
>> +     if (PAGE_SIZE > (1 << 16))
>> +             return -ENOSYS;
>> +
>> +     vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>> +
>> +     uv_mmtimer_addr = UV_LOCAL_MMR_BASE | UVH_RTC;
>> +     uv_mmtimer_addr &= ~(PAGE_SIZE - 1);
>> +     uv_mmtimer_addr &= 0xfffffffffffffffUL;
>> +
>> +     if (remap_pfn_range(vma, vma->vm_start, uv_mmtimer_addr >> PAGE_SHIFT,
>> +                                     PAGE_SIZE, vma->vm_page_prot)) {
>> +             printk(KERN_ERR "remap_pfn_range failed in uv_mmtimer_mmap\n");
>> +             return -EAGAIN;
>> +     }
>> +
>> +     return 0;
>> +}
>
> Methinks we should be setting vma->vm_flags's VM_IO here and perhaps
> also VM_RESERVED.

remap_pfn_range already does it. :)

-- 
Kind regards,
Minchan Kim
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