Hi Robin, On Fri, 21 Apr 2023 15:58:18 +0100 Robin Murphy <robin.murphy@xxxxxxx> wrote: > On 2023-04-21 14:03, Petr Tesařík wrote: >[...] > > Here my question: What did you want for DMA fields? > > > > A. Only grouping those fields in their own struct? > > B. Or move the definition to another include file (cf. MAINTAINERS)? > > C. Or store a pointer in struct device? > > dev->dma_parms is already this, and IIRC still has some very old > comments somewhere about consolidating the other DMA-related fields in > there. Thank you for the hint! I have actually seen dma_parms, but since it can be NULL and was initialized from various drivers, it did not occur to me that NULL simply means not DMA-capable. This is really helpful. Petr T > > Since you mentioned "allocated", it sounds like you want to achieve C, > > but: > > > > 1. Is it worth the extra dereference for every use? > > 2. How should the struct be allocated? Presumably not with kmalloc() in > > device_initialize(), because I don't know how to determine if a > > device is DMA capable this low in the call stack. So, should it be > > allocated together with the containing structure? AFAICS this would > > mean changing nearly all device drivers... > > The bus code knows whether it's a DMA-capable bus or not, and as such > should already be providing a .dma_configure method and/or performing > some initialisation of DMA fields. Many of the ones that would need to > are already providing dma_parms, in fact. > > Thanks, > Robin. > > > > > As you can see, I need some more guidance from you before I can start > > working on this. ;-) > > > > Petr T
