linux-kernel - Re: [PATCH v2 2/6] esp_scsi: Track residual for PIO transfers

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Date:   Mon, 15 Oct 2018 09:14:18 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Michael Schmitz <schmitzmic@...il.com>,
        Hannes Reinecke <hare@...e.de>,
        scsi <linux-scsi@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] esp_scsi: Track residual for PIO transfers

On Sun, 14 Oct 2018, Geert Uytterhoeven wrote:

> 
> > Fixes: 6fe07aaffbf0
> 
> Fixes: 6fe07aaffbf0 ("[SCSI] m68k: new mac_esp scsi driver")
> 

Fixed.

> > Tested-by: Stan Johnson <userm57@...oo.com>
> > Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
> > Tested-by: Michael Schmitz <schmitzmic@...il.com>
> 
> > --- a/drivers/scsi/esp_scsi.h
> > +++ b/drivers/scsi/esp_scsi.h
> > @@ -540,6 +540,8 @@ struct esp {
> >
> >         void                    *dma;
> >         int                     dmarev;
> > +
> > +       int                     send_cmd_residual;
> 
> unsigned int?
> 

My first thought was to use u32, same as esp_count. But it turns out that 
the end result really is an int --

static int esp_data_bytes_sent(struct esp *esp, struct esp_cmd_entry *ent,
                               struct scsi_cmnd *cmd)
{
        int fifo_cnt, ecount, bytes_sent, flush_fifo;

        ...
        bytes_sent = esp->data_dma_len;
        bytes_sent -= ecount;
        bytes_sent -= esp->send_cmd_residual;
	...
        return bytes_sent;
}

Apparently over/underflow is a real possibility, because there is a test 
for this in esp_process_event().

-- 

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>