devm_ioremap() in a sysfs show method
lists at kaiser.cx
Tue May 9 09:47:55 EDT 2017
I've just had another look at this.
Thus wrote Martin Kaiser (lists at kaiser.cx):
> static ssize_t
> my_read_reg(struct device *pdev, struct device_attribute *attr, char *buf)
> u32 __iomem *reg;
> reg = devm_ioremap(pdev, 0x581018C4, 4);
> return scnprintf(buf, PAGE_SIZE, "0x%02x\n", ioread8(reg));
> Is it ok to use devm_ioremap() on the device that I get here? If so, may
> I assume that devm_ioremap() re-uses an existing mapping and it's ok to
> call it for each sysfs access?
Using devm_ioremap() seems a bad idea. I get a different virtual address
in reg for each call to the read method.
Also, using dev_info() or similar debug prints on the device would crash
[ 19.802171] [<c01aa494>] (dev_driver_string+0x0/0x4c) from [<c01aa60c>] (__dev_printk+0x44/0x7c)
[ 19.811011] [<c01aa5c8>] (__dev_printk+0x0/0x7c) from [<c01aa6cc>] (dev_info+0x44/0x50)
[ 19.819117] r6:d388f1a0 r5:d3afd000 r4:d48f68d4
[ 19.823840] [<c01aa688>] (dev_info+0x0/0x50) from [<c0013c6c>] (my_read_reg+0x3c/0x64)
It seems the device that's passed to the read method has some
limitations. In my setup, I created a kobject with NULL parent and
called sysfs_create_group() to attach my nodes to the kobject.
I'd appreciate any hints that help me understand what's going on behind
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