linux-kernel - Re: [PATCH] scsi: lpfc: use memcpy

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Message-ID: <CAK8P3a1--4o7piRf1VEr_cTUaE09ATnWoJfezrg=eqFzM64RoA@mail.gmail.com>
Date:   Fri, 23 Feb 2018 22:02:33 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     James Smart <james.smart@...adcom.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Hannes Reinecke <hare@...e.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scsi: lpfc: use memcpy_toio instead of writeq

On Fri, Feb 23, 2018 at 4:36 PM, Arnd Bergmann <arnd@...db.de> wrote:
> @@ -138,12 +137,10 @@ lpfc_sli4_wq_put(struct lpfc_queue *q, union lpfc_wqe *wqe)
>         if (q->phba->sli3_options & LPFC_SLI4_PHWQ_ENABLED)
>                 bf_set(wqe_wqid, &wqe->generic.wqe_com, q->queue_id);
>         lpfc_sli_pcimem_bcopy(wqe, temp_wqe, q->entry_size);
> -       if (q->dpp_enable && q->phba->cfg_enable_dpp) {
> +       if (q->dpp_enable && q->phba->cfg_enable_dpp)
>                 /* write to DPP aperture taking advatage of Combined Writes */
> -               tmp = (uint8_t *)wqe;
> -               for (i = 0; i < q->entry_size; i += sizeof(uint64_t))
> -                       writeq(*((uint64_t *)(tmp + i)), q->dpp_regaddr + i);
> -       }
> +               memcpy_toio(tmp, q->dpp_regaddr, q->entry_size);
> +
>         /* ensure WQE bcopy and DPP flushed before doorbell write */
>         wmb();
>

Not sure where we are with the question of whether memcpy_toio
is a good replacement or not, but further build testing showed that
my patch was completely broken in more than one way:

I mixed up the source and destination arguments, and I used
the uninitialized 'tmp' instead of 'wqe'. Don't try this patch.

       Arnd