On Mon, Jan 18, 2021 at 03:32:57PM -0500, Al Cooper wrote: > On Mon, Jan 18, 2021 at 12:45 PM Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Fri, Jan 15, 2021 at 04:15:43PM -0500, Al Cooper wrote: > > > Add a UART driver for the new Broadcom 8250 based STB UART. The new > > > UART is backward compatible with the standard 8250, but has some > > > additional features. The new features include a high accuracy baud > > > rate clock system and DMA support. > > > > > > The driver will use the new optional BAUD MUX clock to select the best > > > one of the four master clocks (81MHz, 108MHz, 64MHz and 48MHz) to feed > > > the baud rate selection logic for any requested baud rate. This allows > > > for more accurate BAUD rates when high speed baud rates are selected. > > > > > > The driver will use the new UART DMA hardware if the UART DMA registers > > > are specified in Device Tree "reg" property. The DMA functionality can > > > be disabled on kernel boot with the argument: > > > "8250_bcm7271.disable_dma=Y". > > > > Shouldn't that be on a per-device basis, and not a per-driver basis? > > There is only one instance of the UART DMA hardware and it gets muxed > to just one of the possible UARTS. But the driver doesn't know/care about that, it binds to any device that matches it. per-module/driver flags are not a good idea. > > And why would you want to disable this, if you have support for this in > > the DT? Why not just rely on the DT setting? > > The DMA feature is used when the UART is connected to a Bluetooth > controller and the BAUD rate is typically 2-3Mbs. The ability to > easily disable DMA is very useful when debugging BT communication > problems in the field. DT settings could also be used to disable DMA, > but knowing the correct modifications to the "reg" and "reg-names" > properties is a lot more complicated. So this is a debug-only option? If so, why not just make it a debugfs file then? No need to clutter up a module parameter for this mess. thanks, greg k-h
