Using regmaps to make Linux drivers more generic

Re:Using regmaps to make Linux drivers more generic by londons_explore on Thursday May 28, 2020 @04:50AM (#23334991)

I could see this introducing a performance hit...

Previously a register address was a hardcoded constant. Very small,very fast.

Now, looking up a register ina map involves string matching on the name across every possible register in the map till you find a match. That is much slower, but also makes the kernel quite a lot larger, because you're effectively shipping half the device datasheet in the form of names for every flag bit.

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Re:Using regmaps to make Linux drivers more generic by kanox on Thursday May 28, 2020 @10:28AM (#23337683)

At runtime this is all just a couple of pointer indirections so the impact is minimal. There are also special functions for bulk transfer so regmap shouldn't be called in tight loops.

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Re:Using regmaps to make Linux drivers more generic by akx on Thursday May 28, 2020 @06:51AM (#23335818)

There's no string matching that I can see in the linked article?

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Re:Using regmaps to make Linux drivers more generic by londons_explore on Thursday May 28, 2020 @09:36AM (#23337054)

" .name = "dw-mipi-dsi","

Looks like a string in the structure to me. And when you have an array of such structures, you end up scanning through them checking for the name you need.

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Re:Using regmaps to make Linux drivers more generic by akx on Thursday May 28, 2020 @09:43AM (#23337104)

That's the name of the regmap. Clicking through to the definition of the structure says it's optional and thus there for descriptive purposes.

     *
     * @name: Optional name of the regmap. Useful when a device has multiple
     *        register regions.

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Re:Using regmaps to make Linux drivers more generic by cesarb on Thursday May 28, 2020 @09:47AM (#23337157)

Look at the usage example a couple of lines below; it's passing a pointer to that structure. There's no scanning necessary, it already knows where the structure is.

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