---- On Wed, 27 May 2015 17:10:06 -0700 Guenter Roeck<linux@xxxxxxxxxxxx> wrote ---- > On 05/27/2015 04:58 PM, andrey wrote: > > > > > > ---- On Wed, 27 May 2015 16:08:12 -0700 Guenter Roeck<linux@xxxxxxxxxxxx> wrote ---- > > > > > On 05/27/2015 12:44 PM, andrey wrote: > > > > Hello all, > > > > Let me add a comment on using sysfs to simplify user space access to the clock > > > > features as opposed to controlling them from a driver that uses the clock chip driver. > > > > > > > > It is common to use such advanced clock chips with the FPGA devices (as me and > > > > York do), and a lot of development (HDL code) is done before a fancy higher-level > > > > driver is even started. And it is not just a temporary stage needed by a small minority > > > > of developers - as HDL coding gets more to the the core of many new devices running > > > > Linux kernel, it makes sense to create the chip drivers more developer-friendly, not > > > > just for the final use in a higher level device driver - modification of the HDL code > > > > (most modern FPGA are programmed at runtime) makes it a new device that may > > > > need a new driver. > > > > I'm sure that it is not just for me, when it starts with the chip driver that supports > > > > low-level functionality exposing it to the user space, and then working on the HDL > > > > code using Python scripts at that stage. And only later in the development designing > > > > the higher level device drivers that may not need all of the chip functionality. And such > > > > higher level driver will work for our systems, but other developers who work on their > > > > embedded systems will again need access to low level chip functionality, and will have > > > > to redo the same work all over again. This I believe is a rationale of exposing such > > > > chip-specific hardware features (not all of them are probably easy to fit into a specific > > > > standard model) to the user space scripts. > > > > > > > > I wrote the initial driver code for our system > > > > ( https://github.com/Elphel/linux-elphel/blob/master/src/drivers/misc/si5338.c ) and > > > > being very far from being a kernel developer myself (I'm more of a hardware guy) > > > > I didn't even try to satisfy the required coding style and submit it, so I'm very thankful > > > > to York who re-wrote the code and is trying to make it usable to others. > > > > > > > > > > Line wraps at ~75 columns would make this a bet easier to read. > > > > Guenter, I'm sorry for using "rich text" email settings. > > > > > > > > A more generic solution to your problem might be to implement a driver > > > similar to i2c-dev, which exports raw i2c device information to user space. > > > In your case, you would export information about the clocks in the system, > > > possibly through sysfs (i2c-dev uses ioctl which is a bit old-fashioned). > > > > I was trying to make it safer to use low-level functionality of the particular > > (and rather popular) clock chip and to avoid using SiLabs proprietary tools to > > generate required settings offline. Using just raw i2c would require to have > > large user space program to calculate valid settings for the device. > > > > I would consider this chip as both a generic clock device that can fit into > > a standard framework and simultaneously a unique device that offers specific > > functionality outside of the framework. I thought that sysfs (instead of > > "old-fashioned" ioctl I used in such cases before) can offer > > hardware developer-friendly solution as a supplement to in-framework > > basic functionality. > > > > Device driver for this chip makes it possible to avoid proprietary configuration > > software and calculate register settings at runtime, minimizing requirements to > > the user space software and so the time developers of the new embedded > > systems will need to (re-)implement these important chip-specific features. > > > > I think we are in violent agreement ;-). Only question was how to implement > sysfs (or user space access) support, where my preference would be a more > generic solution. Guenter, I just considered this chip as a "frontier" device, not yet a member of an established class of similar ones. It may be possible to generalize later, extracting common functionality to a more abstract interface. But we just need this device support now, and when this one will become a member of some generic class - "frontier" will again move a step farther, new devices will emerge that stick out of the nice frameworks. Andrey > > Thanks, > Guenter > > > Andrey > > > > > > > > This would be a driver independent solution, and work for all clock drivers. > > > It might still not be accepted by Mike and Stephen, due to the risk, but it > > > might be worth a try. After all, using i2c-dev to access i2c devices directly > > > is just as risky. > > > > > > In my opinion, it is always better to have a driver in the upstream kernel, > > > if possible one that uses a standard framework. That makes it much easier > > > to support going forward. > > > > > > Guenter > > > > > > > > > > > > > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
