Re: [PATCH v1 11/11] mmc: mmci: Add Qcom specific pio_read function.

[Srinivas Kandagatla]

On 13/05/14 09:34, Linus Walleij wrote:
> On Tue, Apr 29, 2014 at 10:21 AM,  <srinivas.kandagatla@xxxxxxxxxx> wrote:
>
> > From: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> >
> > MCIFIFOCNT register behaviour on Qcom chips is very different than the other
> > pl180 integrations. MCIFIFOCNT register contains the number of
> > words that are still waiting to be transferred through the FIFO. It keeps
> > decrementing once the host CPU reads the MCIFIFO. With the existing logic and
> > the MCIFIFOCNT behaviour, mmci_pio_read will loop forever, as the FIFOCNT
> > register will always return transfer size before reading the FIFO.
> >
> > Also the data sheet states that "This register is only useful for debug
> > purposes and should not be used for normal operation since it does not reflect
> > data which may or may not be in the pipeline".
> >
> > This patch implements qcom_pio_read function so as existing mmci_pio_read is
> > not suitable for Qcom SOCs.
> >
> > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> (...)
>
> > +static int mmci_qcom_pio_read(struct mmci_host *host, char *buffer,
> > +                        unsigned int remain)
> > +{
> > +       uint32_t        *ptr = (uint32_t *) buffer;
>
> Just use u32 for this.
>
> > +       int             count = 0;
> > +       struct variant_data *variant = host->variant;
> > +       int             fifo_size = variant->fifosize;
> > +
> > +       if (remain % 4)
> > +               remain = ((remain >> 2) + 1) << 2;
>
> Explain in a comment exactly what is happening here or noone will
> understand the code.

Ok, I will add more comments here.
> > +       while (readl(host->base + MMCISTATUS) & MCI_RXDATAAVLBL) {
> > +               *ptr = readl(host->base + MMCIFIFO + (count % fifo_size));
> > +               ptr++;
> > +               count += sizeof(uint32_t);
> > +               remain -=  sizeof(uint32_t);
>
>
> sizeof(u32) or just 4 works for these...
Yes, Will fix it in next version.
> count += 4;
> remain -= 4;
>
> Is easier to parse and understand I think.
>
> > +               if (remain == 0)
> > +                       break;
>
> if (!remain)
>    break;
yep.

> > +       }
> > +       return count;
> > +}
>
> > -               if (status & MCI_RXACTIVE)
> > -                       len = mmci_pio_read(host, buffer, remain);
> > +               if (status & MCI_RXACTIVE) {
> > +                       if (host->hw_designer == AMBA_VENDOR_QCOM)
> > +                               len = mmci_qcom_pio_read(host, buffer, remain);
> > +                       else
> > +                               len = mmci_pio_read(host, buffer, remain);
> > +               }
>
> Use something like bool qcom_fifo; in vendor data instead.
Ok, make sense, I will fix this in next version.

--srini

> Yours,
> Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/