Messages in this thread | | | Date | Fri, 5 Dec 2008 16:32:30 -0800 | From | "Edward Estabrook" <> | Subject | Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA |
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> Well, UIO already rapes the mmap interface by using the "offset" parameter to > pass in the number of the mapping.
Exactly.
> But I'll NAK the current concept, too. It's a UIO kernel driver's task to tell > userspace which memory a device has to offer. The UIO core prevents userspace > as much as possible from mapping anything different. And it should stay that > way.
The ultimate purpose (I thought) of the UIO driver is to simplify driver development by pushing device control into userspace. There is a very real need for efficient dynamic control over the DMA allocation of a device. Why not 'allow' this to happen in userspace if it can be done safely and without breaking anything else?
Remember that for devices employing ring buffers it is not a question of 'how much memory a device has to offer' but rather 'how much system memory would the driver like to configure that device to use'.
I don't want to stop my DMA engine and reload the driver to create more buffers (and I don't want to pre-allocate more than I need as contingency).
Cheers, Ed
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