linux-kernel - Re: [PATCH 3/3] alpha, drm: Add Alpha support to Radeon DRM code

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Date:	Tue, 14 Jun 2011 22:38:10 -0400
From:	Jay Estabrook <jay.estabrook@...il.com>
To:	Dave Airlie <airlied@...il.com>
CC:	linux-alpha <linux-alpha@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Matt Turner <mattst88@...il.com>,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>, airlied@...ux.ie
Subject: Re: [PATCH 3/3] alpha, drm: Add Alpha support to Radeon DRM code

Hi, Dave,

It is the explanation that is inaccurate; I was still thinking about mmap when
the new paradigm is to do the mapping when the VM faults.

I believe the code that requires this patch is: ttm/ttm_bo_vm.c: ttm_bo_vm_fault(),
specifically:

    for (i = 0; i < TTM_BO_VM_NUM_PREFAULT; ++i) {
        if (bo->mem.bus.is_iomem)
            pfn = ((bo->mem.bus.base + bo->mem.bus.offset) >> PAGE_SHIFT) + page_offset;
        else {

The "pfn" needs to reflect the correct system bus address to get to the VRAM
on the graphics card.

I will rework the commentary and resend.

Thanks for the feedback.

Jay


On 06/13/2011 07:35 PM, Dave Airlie wrote:
> On Fri, Jun 10, 2011 at 8:20 AM, Jay Estabrook <jay.estabrook@...il.com> wrote:
>> Alpha needs to have the system bus address for the device's local
>> memory available, so that it can be returned to user-level, where
>> it may be used in an mmap(). So, we make bus.addr hold the ioremap()
>> return for kernel use, and then we can modify bus.base appropriately.
>>
> 
> I don't get this. why is mmap passing in an address? we don't do that anymore.
> 
> When you mmap the device node it passes back a hashed offset in the
> table, that the
> kernel then translates into a proper address and sets up the page tables.
> 
> So I really don't get what this patch is doing, either the
> explaination of what it is doing is wrong
> or it is wrong.
> 
> Dave.
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