Re: Copying user space data to PCI memory

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On Mon, May 18, 2009 at 6:50 AM, Grant Grundler
<grundler@xxxxxxxxxxxxxxxx> wrote:
> Hi Arun, Sandeep,
>
> On Sat, May 16, 2009 at 06:33:44PM +0530, SandeepKsinha wrote:
>> Hi Arun,
>>
>> On Sat, May 16, 2009 at 5:48 PM, arun c <arun.edarath@xxxxxxxxx> wrote:
>> > Hi all,
>> >
>> > I want to copy data from user space to PCI memory.
>> >
>> > I mapped the PCI memory of the card by,
>> >
>> > 1)pci_request_regions(pci_dev, DEVICE_NAME);
>> > 2)buffer_addr = pci_iomap(pci_dev, 1, 1024);
>> >
>> > Now I want to write data supplied by the
>> > user to buffer_addr(BAR1 pre-fetch-able memory
>> > of the device)
>> >
>> > I did like this:
>> >
>> > copy_from_user(buffer_addr, usr_addr, 1024)
>> >
>> > This method is working fine on an X86 running
>> > linux 2.6.27 kernel. I can see the data clearly copied.
>> >
>> > I want to know is this legal for all the platforms? and for
>> > older kernels starting from 2.6.16?
>> >
>> > If the above method is totally legal then can I use
>> > copy_to_user(usr_addr, buffer_addr, 1024) also?
>>
>> AFAIK, yes.
>
> Sorry, I don't think so.
>
> Copying stuff to non-cacheable addresses can have other side effects.
> So the optimizations available when copying TO cacheable address space
> are generally not available (or have risks).
>

I totally agree with this.

> That's why we have copy_from_user_toio()
>   http://www.digipedia.pl/man/copy_from_user_toio.9.html
>

Remember that there are various flavours of it and each one has its
own specific use. Arun's question was not very specific to a
situation, it was generic.
If needed, he can always look at the other flavours of copy_to/from_user.
.

> hth,
> grant
>



-- 
Regards,
Sandeep.





 	
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