Hi Gabriel, On Tue, Dec 7, 2021 at 10:30 PM Gabriel L. Somlo <gsomlo@xxxxxxxxx> wrote: > 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>; > }; > ... > }; LGTM. > 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); Please use ret = dev_err_probe(&pdev->dev, PTR_ERR(clk), "can't get clock\n"); to avoid printing the error in case of probe deferral. > 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. Nice, that's a good solution, until the full clock tree is exposed in the DTS. Thanks a lot! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
