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SubjectRe: [PATCH RFC] spidev.c: add sysfs attributes for SPI configuration
Date
> I'm cautious about adding operational interfaces to sysfs because it
> can be quite difficult to get the locking right. To begin with it
> splits up a single interface into multiple files, any of which can
> be held open by a process. Then there is the question of ordering
> of operations when there are multiple users. For instance, if there
> were two users, each of which using different transfer parameters,
> a sysfs interface doesn't provide any mechanism to group setting up
> the device with the transfer.
>
> These are lessons learned the hard way with the gpio sysfs abi. I
> don't want to get caught in the same trap for spi.
>
> g.

I understand the problem, but I think that for very simple test on
devices, sysfs is easier. For example, it happens that a SPI device
does not work correctly with a driver, so I want to verify the SPI
traffic by writing directly the device commands and check with an
oscilloscope. I think that an easy way is to use sysfs like this:

echo 123456 > speed_hz
[other options if needed]
echo -n -e "\x12\x34" > /dev/spidev1.1
[oscilloscope]
hexdump -n 2 /dev/spidev1.1

This sysfs interface should be used only for testing/debugging, not to
develop an user space driver on it; moreover, the ioctl interface is
still there.

spidev_test and spidev_fdx does not allow me to customize tx buffer and
I think (very personal opinion) that for debugging purpose is better
sysfs with well known programs (echo, cat, hexdump, od) and
oscilloscope.

I know that I'm not so persuasive :) I can develop a simple program
that can write custom tx buf with ioctl

--
Federico Vaga


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