On Mon, Oct 9, 2023 at 3:04 PM Wilczynski, Michal <michal.wilczynski@xxxxxxxxx> wrote: > > > > On 10/9/2023 2:27 PM, Rafael J. Wysocki wrote: > > On Mon, Oct 9, 2023 at 10:40 AM Wilczynski, Michal > > <michal.wilczynski@xxxxxxxxx> wrote: > >> [cut] > >> Yeah we could add platform device without removing acpi device, and > >> yes that would introduce data duplication, like Andy noticed. > > But he hasn't answered my question regarding what data duplication he > > meant, exactly. > > > > So what data duplication do you mean? > > So what I meant was that many drivers would find it useful to have > a struct device embedded in their 'private structure', and in that case > there would be a duplication of platform_device and acpi_device as > both pointers would be needed. It all depends on how often each of them is going to be used in the given driver. This particular driver only needs a struct acpi_device pointer if I'm not mistaken. > Mind this if you only have struct device > it's easy to get acpi device, but it's not the case the other way around. > > So for this driver it's just a matter of sticking to convention, There is no convention in this respect and there is always a tradeoff between using more memory and using more CPU time in computing in general, but none of them should be wasted just for the sake of following a convention. > for the others like it would be duplication. So I'm only talking about the driver modified by the patch at hand. > In my version of this patch we managed to avoid this duplication, thanks > to the contextual argument introduced before, but look at this patch: > https://github.com/mwilczy/linux-pm/commit/cc8ef52707341e67a12067d6ead991d56ea017ca > > Author of this patch had to introduce platform_device and acpi_device to the struct ac, so > there was some duplication. That is the case for many drivers to come, so I decided it's better > to change this and have a pattern with keeping only 'struct device'. Well, if the only thing you need from a struct device is its ACPI_COMPANION(), it is better to store a pointer to the latter.
