netdev - Re: [PATCH v3 rdma-next 0/3] RDMA/qedr: Use the doorbell overflow recovery mechanism for RDMA

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Date:   Fri, 21 Jun 2019 16:58:18 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Michal Kalderon <mkalderon@...vell.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        Ariel Elior <aelior@...vell.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 rdma-next 0/3] RDMA/qedr: Use the doorbell overflow
 recovery mechanism for RDMA

On Fri, Jun 21, 2019 at 07:49:39PM +0000, Michal Kalderon wrote:
> > From: linux-rdma-owner@...r.kernel.org <linux-rdma-
> > owner@...r.kernel.org> On Behalf Of Doug Ledford
> > 
> > On Thu, 2019-06-13 at 11:38 +0300, Michal Kalderon wrote:
> > > This patch series used the doorbell overflow recovery mechanism
> > > introduced in commit 36907cd5cd72 ("qed: Add doorbell overflow
> > > recovery mechanism") for rdma ( RoCE and iWARP )
> > >
> > > rdma-core pull request #493
> > >
> > > Changes from V2:
> > > - Don't use long-lived kmap. Instead use user-trigger mmap for the
> > >   doorbell recovery entries.
> > > - Modify dpi_addr to be denoted with __iomem and avoid redundant
> > >   casts
> > >
> > > Changes from V1:
> > > - call kmap to map virtual address into kernel space
> > > - modify db_rec_delete to be void
> > > - remove some cpu_to_le16 that were added to previous patch which are
> > >   correct but not related to the overflow recovery mechanism. Will be
> > >   submitted as part of a different patch
> > >
> > >
> > > Michal Kalderon (3):
> > >   qed*: Change dpi_addr to be denoted with __iomem
> > >   RDMA/qedr: Add doorbell overflow recovery support
> > >   RDMA/qedr: Add iWARP doorbell recovery support
> > >
> > >  drivers/infiniband/hw/qedr/main.c          |   2 +-
> > >  drivers/infiniband/hw/qedr/qedr.h          |  27 +-
> > >  drivers/infiniband/hw/qedr/verbs.c         | 387
> > > ++++++++++++++++++++++++-----
> > >  drivers/net/ethernet/qlogic/qed/qed_rdma.c |   6 +-
> > >  include/linux/qed/qed_rdma_if.h            |   2 +-
> > >  include/uapi/rdma/qedr-abi.h               |  25 ++
> > >  6 files changed, 378 insertions(+), 71 deletions(-)
> > >
> > 
> > Hi Michal,
> > 
> > In patch 2 and 3 both, you still have quite a few casts to (u8 __iomem *).
> > Why not just define the struct elements as u8 __iomem * instead of void
> > __iomem * and avoid all the casts?
> > 
> Hi Doug, 
> 
> Thanks for the review. The remaining casts are due to pointer arithmetic and not variable assignments
> as before. Removing the cast entirely will require quite a lot of changes in qed and in rdma-core
> which I would be happy to avoid at this time. 

In linux pointer math on a void * acts the same as a u8 so you should
never need to cast a void * to a u8 just to do math?

Jason