Re: [PATCH 15/23] seq_file: switch over direct seq_read method calls to seq_read_iter

[Christoph Hellwig]

On Fri, Jul 10, 2020 at 01:55:29PM +0100, Jon Hunter wrote:
> Following this change, I have noticed that several debugfs entries can
> no longer be read on some Tegra platforms. For example ...
> 
> $ sudo cat /sys/kernel/debug/usb/xhci/3530000.usb/event-ring/cycle
> cat: /sys/kernel/debug/usb/xhci/3530000.usb/event-ring/cycle: Invalid
> argument
> 
> $ sudo cat /sys/kernel/debug/emc/available_rates
> 
> 
> cat: /sys/kernel/debug/emc/available_rates: Invalid argument
> 
> $ sudo cat /sys/kernel/debug/bpmp/debug/proc/testint
> cat: /sys/kernel/debug/bpmp/debug/proc/testint: Invalid argument
> 
> $ sudo cat /sys/kernel/debug/pcie/ports
> 
> 
> cat: /sys/kernel/debug/pcie/ports: Invalid argument
> 
> I have reverted the above drivers to use seq_read() instead of
> seq_read_iter() and they work again. Have you seen any problems with this?

I haven't seen any of that.  But some of these files should also
exist on x86, so let me try to reproduce it.