Messages in this thread | | | Subject | Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability | From | Lu Baolu <> | Date | Thu, 10 Nov 2016 09:13:16 +0800 |
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Hi,
On 11/09/2016 05:23 PM, Thomas Gleixner wrote: > On Tue, 1 Nov 2016, Lu Baolu wrote: >> +static int __init xdbc_init(void) >> +{ > ... >> + base = ioremap_nocache(xdbc.xhci_start, xdbc.xhci_length); >> + if (!base) { >> + xdbc_trace("failed to remap the io address\n"); >> + ret = -ENOMEM; >> + goto free_and_quit; >> + } >> + >> + early_iounmap(xdbc.xhci_base, xdbc.xhci_length); >> + xdbc_trace("early mapped IO address released\n"); >> + >> + xdbc.xhci_base = base; >> + offset = xhci_find_next_ext_cap(xdbc.xhci_base, 0, XHCI_EXT_CAPS_DEBUG); >> + xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset); > This is broken. What prevents that > > - a printk is in progress on another cpu? > > - a printk happens between the unmap and storing the new base ? > > Nothing AFAICT. So this needs to be done in a safe way. And just making it > > oldbase = xdbc.xhci_base; > base = ioremap(....); > xdbc.xhci_base = base; > early_iounmap(oldbase); > > does not work either because the compiler can rightfully cache > xdbc.xhci_base in the write related functions. The same issue with > xdbc.xdbc_reg.
If there isn't a good solution, I will remove the ioremap code and let it use the early mapped one.
Best regards, Lu Baolu
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