On 23/05/14 10:31, Linus Walleij wrote:
On Thu, May 15, 2014 at 11:38 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. qcom_pio_read function is only selected
based on qcom_fifo flag in variant data structure.
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;
Oops..
Sorry Linus, I think this change-set got something different than what I
did. I remember your comments in the last review, I did take care of
them but some how It got missed... I will fix these and send a new version.
Just use u32 like the rest of the driver does.
+ int fifo_size = variant->fifosize;
+
+ if (remain % 4)
And another variant is to count the *number or words*
to read from the FIFO rather than the number of bytes! I would do it
like this:
static int mmci_qcom_pio_read(struct mmci_host *host, char *buffer,
unsigned int remain)
{
u32 *ptr = (u32*) buffer;
unsigned int count = 0;
unsigned int words;
unsigned int fifo_size = host->variant->fifosize;
words = DIV_ROUND_UP(remain, 4);
while (readl(host->base + MMCISTATUS) & MCI_RXDATAAVLBL) {
*ptr = readl(host->base + MMCIFIFO + (count % fifo_size));
ptr++;
count += 4;
remain--;
if (!remain)
break;
}
return count;
}
I guess you will run into additional problems when you come to doing
SDIO. This function can return *more* bytes than asked for, as it rounds
up. It won't happen with MMC/SD transfers since these are always
divisible by 8, but it *will* happen on SDIO!
If you look carefully at the comments in mmci_pio_read() you will
see how this is handled. Are you sure this function cannot be
augmented to handle the qcom variant as well so you don't get this
problem further down the road?
I did try to customize the mmci_pio_read function but I failed all the
time. The reason being the behaviour of MCI_FIFOCNT register which is
totally different to the way the function is written. I will give a try
again.
Thanks,
srini
Yours,
Linus Walleij
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