On 8/17/22 21:18, Xu Yilun wrote: > On 2022-08-17 at 17:37:46 -0400, Peter Colberg wrote: >> Add a Device Feature List (DFL) feature id for the configurable >> IOPLL user clock source, which can be used to configure the clock >> speeds that are used for RTL logic that is programmed into the >> Partial Reconfiguration (PR) region of an FPGA. > Why not use linux clock framework for this IOPLL? And let the PR > driver set it togeter with the RTL logic reporgramming? Hi Yilun, We previously explored the possibility of plugging into the linux clock framework. For this device, setting a desired frequency is heavily dependent on a table of values that must be programmed in order to achieve the desired clock speeds. Here is an example table, indexed by frequency. The first element in each entry is the frequency in kHz: https://github.com/OPAE/opae-sdk/blob/master/libraries/plugins/xfpga/usrclk/fpga_user_clk_freq.h We previously experimented with a kernel-space driver. The implementation exported a sysfs node into which the table values for the desired frequency would be written in order to set the desired frequency. The function of the driver was to execute the logic required to program the device. We did not think this implementation should be up-streamed. It isn't practical to upstream the frequency tables as they are subject to change for future devices. For example, if the reference frequency changed in a future device, a whole new table of values would have to be added for the new device. In a recent transition to a new device, the range of frequencies was increased which required an extension to an existing table. A previous implementation of the user clock was also implemented in user-space. The kernel driver exported each of the registers, but all of the logic was implemented in user-space. The kernel portion can be viewed here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/fpga/dfl-afu-main.c#n380 This is our reasoning in choosing to implement this driver in user-space. Would you consider a uio based user-space driver to be acceptable for in this case? - Russ > > Thanks, > Yilun > >> The DFL feature id table can be found at: >> https://github.com/OPAE/dfl-feature-id >> >> Signed-off-by: Peter Colberg <peter.colberg@xxxxxxxxx> >> --- >> drivers/uio/uio_dfl.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/drivers/uio/uio_dfl.c b/drivers/uio/uio_dfl.c >> index 8f39cc8bb034..69e93f3e7faf 100644 >> --- a/drivers/uio/uio_dfl.c >> +++ b/drivers/uio/uio_dfl.c >> @@ -46,10 +46,12 @@ static int uio_dfl_probe(struct dfl_device *ddev) >> >> #define FME_FEATURE_ID_ETH_GROUP 0x10 >> #define FME_FEATURE_ID_HSSI_SUBSYS 0x15 >> +#define PORT_FEATURE_ID_IOPLL_USRCLK 0x14 >> >> static const struct dfl_device_id uio_dfl_ids[] = { >> { FME_ID, FME_FEATURE_ID_ETH_GROUP }, >> { FME_ID, FME_FEATURE_ID_HSSI_SUBSYS }, >> + { PORT_ID, PORT_FEATURE_ID_IOPLL_USRCLK }, >> { } >> }; >> MODULE_DEVICE_TABLE(dfl, uio_dfl_ids); >> -- >> 2.28.0 >>
