Hi Geert, I think I figured out a solution, see below: On Tue, Dec 07, 2021 at 03:16:22PM +0100, Geert Uytterhoeven wrote: > On Tue, Dec 7, 2021 at 3:10 PM Gabriel L. Somlo <gsomlo@xxxxxxxxx> wrote: > > On Mon, Dec 06, 2021 at 01:24:49PM +0100, Geert Uytterhoeven wrote: > > > On Sat, Dec 4, 2021 at 9:41 PM Gabriel Somlo <gsomlo@xxxxxxxxx> wrote: > > > > LiteX (https://github.com/enjoy-digital/litex) is a SoC framework > > > > that targets FPGAs. LiteSDCard is a small footprint, configurable > > > > SDCard core commonly used in LiteX designs. > > > > > > > > The driver was first written in May 2020 and has been maintained > > > > cooperatively by the LiteX community. Thanks to all contributors! > > > > > > > > Co-developed-by: Kamil Rakoczy <krakoczy@xxxxxxxxxxxx> > > > > Signed-off-by: Kamil Rakoczy <krakoczy@xxxxxxxxxxxx> > > > > Co-developed-by: Maciej Dudek <mdudek@xxxxxxxxxxxxxxxxxxxxxxxx> > > > > Signed-off-by: Maciej Dudek <mdudek@xxxxxxxxxxxxxxxxxxxxxxxx> > > > > Co-developed-by: Paul Mackerras <paulus@xxxxxxxxxx> > > > > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx> > > > > Signed-off-by: Gabriel Somlo <gsomlo@xxxxxxxxx> > > > > > + host->clock = 0; > > > > + cpu = of_get_next_cpu_node(NULL); > > > > + ret = of_property_read_u32(cpu, "clock-frequency", &host->freq); > > > > + of_node_put(cpu); > > > > + if (ret) { > > > > + dev_err(&pdev->dev, "No \"clock-frequency\" property in DT\n"); > > > > + goto err_free_host; > > > > + } > > > > > > This looks fragile. > > > Shouldn't the clock be obtained from a clock property in the mmc > > > device node, pointing to a clock provider? > > > How does the real clock tree look like? > > > > In a full LiteX SoC, the main sys_clock is used for cpu, buses, and as a > > input source for peripherals such as LiteSDCard (which then further > > subdivides it to obtain a 12.5--50.0 MHz sd_clock. > > > > But since we're considering supporting LiteSDCard as an independent IP > > block, the "source clock" frequency should indeed be specified as a DT > > property in the MMC device node. (I'll have to add that to the list of > > updates for litex_json2dts_linux.py as well, once we settle on what it > > will look like -- I'll try to make the change and corresponding update > > to the devicetree bindings doc for v3). > > > > LMK what you think. > > Ideally there should be a "clocks" property with a phandle pointing to a > clock controller node (compatible with "litex,clk"). > > How does drivers/tty/serial/liteuart.c handle this? Oh, it doesn't ;-) Assuming LiteX's `litex_json2dts_linux.py` is modified to include: ... clocks { sys_clk: litex_sys_clk { #clock-cells = <0>; compatible = "fixed-clock"; clock-frequency = <50000000>; }; }; ... in the generated .dts (where `clock-frequency` is whatever the sys_clk happens to be for that particular SoC gateware), we can then write the mmc node like so: soc { ... mmc0: mmc@12005000 { compatible = "litex,mmc"; reg = <0x12005000 0x100>, <0x12003800 0x100>, <0x12003000 0x100>, <0x12004800 0x100>, <0x12004000 0x100>; reg-names = "phy", "core", "reader", "writer", "irq"; clocks = <&sys_clk>; interrupt-parent = <&L1>; interrupts = <4>; }; ... }; The LiteSDCard clock initialization can then look like this: ... /* initialize clock source */ clk = devm_clk_get(&pdev->dev, NULL); if (IS_ERR(clk)) { ret = PTR_ERR(clk); dev_err(&pdev->dev, "can't get clock: %d\n", ret); goto err; } host->freq = clk_get_rate(clk); /* source (sys_clock) frequency */ host->clock = 0; /* calculated sdclock frequency */ ... As discussed before, I'll post a `litex_json2dts_linux.py` patch once we've settled on a mutually agreeable solution, but I think this might be it. If you agree, I'll also update the DT binding document to require `clocks` as part of the mmc node. I tested this in my v3 candidate, and it seems to be working OK. LMK what you think, and/or if you have any suggestions for additional improvements. Thanks again, --Gabriel
