Re: [PATCH] scsi: mpt3sas: clarify mmio pointer types

[Martin K. Petersen]

Broadcom folks: Please review!

> The newly added code mixes up phys_addr_t/resource_size_t with dma_addr_t
> and void pointers, as seen from these compiler warning:
>
> drivers/scsi/mpt3sas/mpt3sas_base.c: In function '_base_get_chain_phys':
> drivers/scsi/mpt3sas/mpt3sas_base.c:235:21: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>   base_chain_phys  = (void *)ioc->chip_phys + MPI_FRAME_START_OFFSET +
>                      ^
> drivers/scsi/mpt3sas/mpt3sas_base.c: In function '_clone_sg_entries':
> drivers/scsi/mpt3sas/mpt3sas_base.c:427:20: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>     sgel->Address = (dma_addr_t)dst_addr_phys;
>                     ^
> drivers/scsi/mpt3sas/mpt3sas_base.c:438:7: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>        (dma_addr_t)buff_ptr_phys;
>        ^
> drivers/scsi/mpt3sas/mpt3sas_base.c:444:10: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>           (dma_addr_t)buff_ptr_phys;
>
> Both dma_addr_t and phys_addr_t may be wider than a pointer, so we must
> avoid the conversion to pointer types. This also helps readability.
>
> A second problem is treating MMIO addresses from a 'struct resource'
> as addresses that can be used for DMA on that device. In almost all
> cases, those are the same, but on some of the more obscure architectures,
> PCI memory address 0 is mapped into the CPU address space at a nonzero
> offset. I don't have a good fix for that, so I'm adding a comment here,
> plus a WARN_ON() that triggers whenever the phys_addr_t number is
> outside of the low 32-bit address space and causes a straight overflow
> when assigned to the 32-bit sgel->Address.

-- 
Martin K. Petersen	Oracle Linux Engineering