Re: A simple EPICS driver example for PCI devices using asynPortDriver on Linux

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

On 12/4/22 02:39, Perez Juarez, Emilio (DLSLtd, RAL, LSCI) via Tech-talk wrote:
> Hi Lin Wang and thanks for sharing,
>
> I have some comments/questions:
>
>   * Is there a reason why you prefer to use ioctl for register access instead of mmap and letting userspace access directly?
>   * I know security is usually not a priority, but I've noticed you don't check/validate the register offset passed in the ioctl syscall, which means it could give access to other resources (memory or I/O)
>   * You might want to provide a fallback path when the target system doesn't have your kernel module installed, in which case, you can get register access by mmap'ing /sys/bus/pci/devices/<X>/resource<Y>, where <X> is the domain:bus:devices.function of your device and <Y> is the BAR number you want to access
>   * I noticed you dereference a volatile pointer to access the registers, in kernel space I'd recommend using the functions ioread<X> or iowrite<X> instead, where <X> is the access size (8, 16 or 32). This will make code more portable.
Sorry, I didn't notice this thread sooner.

My devlib2 support module does just what is described, and is portable
across Linux, RTEMS, and vxWorks.

https://epics.sourceforge.net/devlib2/

https://github.com/epics-modules/devlib2

This includes device support for simple register operations.

https://epics.sourceforge.net/devlib2/exploreapp.html

No DMA support, but there is limited support for interrupts if a
device supports the standard INTx Disable bit in the PCI_CONFIG
register (not to be assumed).

https://epics.sourceforge.net/devlib2/exploreapp.html#exploreirq


> I hope any of that was useful,
>
> Kind Regards,
> Emilio
>
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> *From:* Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Wang, Lin via Tech-talk <tech-talk at aps.anl.gov>
> *Sent:* 02 December 2022 10:15
> *To:* tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
> *Subject:* A simple EPICS driver example for PCI devices using asynPortDriver on Linux
>
> Dear all,
>
>
> A simple EPICS driver example for PCI devices using asynPortDriver on Linux is shared in the following GitHub link in case somebody might be interested,
>
> https://github.com/wanglin86769/cpciEpicsApp
>
>
> This is an EPICS IOC developed for the LLRF system of a small-scale accelerator facility at CSNS campus. The LLRF board is a customized cPCI FPGA board with PCI 9056 bridge, the control interface is merely register access plus waveform read with 1 second update period, no interrupt or DMA is needed.
>
>
> The Linux driver part is implemented as kernel module rather than UIO (Userspace I/O). This example is only useful for simple customized PCI devices that does not need interrupt and DMA, and only one MMIO (Memory mapped I/O) BAR is used to access the FPGA registers.
>
>
> This is my first assignment to control PCI under Linux rather than vxWorks, any suggestion is appreciated.
>
>
>
> Regards,
>
> Lin Wang
>
> Staff Engineer
>
> Controls Group, Accelerator System Division, CSNS (China Spallation Neutron Source)
>
> IHEP (Institute of High Energy Physics), Chinese Academy of Science
>
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