linux-kernel - Re: [PATCH] scsi: mpt3sas: clarify mmio pointer types

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Date:   Thu, 01 Mar 2018 20:59:05 -0500
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Suganath Prabu S <suganath-prabu.subramani@...adcom.com>,
        Sathya Prakash <sathya.prakash@...adcom.com>,
        Chaitra P B <chaitra.basappa@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Hannes Reinecke <hare@...e.de>,
        Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
        MPT-FusionLinux.pdl@...adcom.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: mpt3sas: clarify mmio pointer types


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