linux-kernel - Re: [Outreachy kernel] Re: [PATCH v2 4/6] staging: fbtft: Fix sparse warnings of incorrect type in assignment

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Date:   Sun, 5 Mar 2017 10:10:30 +0530
From:   SIMRAN SINGHAL <singhalsimran0@...il.com>
To:     Alison Schofield <amsfield22@...il.com>
Cc:     Noralf Trønnes <noralf@...nnes.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        sergio.paracuellos@...il.com,
        Juliana Rodrigues <juliana.orod@...il.com>,
        thomas.petazzoni@...e-electrons.com,
        outreachy-kernel@...glegroups.com
Subject: Re: [Outreachy kernel] Re: [PATCH v2 4/6] staging: fbtft: Fix sparse
 warnings of incorrect type in assignment

On Sun, Mar 5, 2017 at 5:36 AM, Alison Schofield <amsfield22@...il.com> wrote:
> On Thu, Mar 02, 2017 at 02:26:37PM +0100, Noralf Trønnes wrote:
>>
>> Den 02.03.2017 14.04, skrev simran singhal:
>> >This patch fixes the following sparse warnings:
>> >
>> >drivers/staging/fbtft/fbtft-bus.c:166:36: warning: incorrect type in assignment (different base types)
>> >drivers/staging/fbtft/fbtft-bus.c:166:36:    expected unsigned short [unsigned] [short] [usertype] <noident>
>> >drivers/staging/fbtft/fbtft-bus.c:166:36:    got restricted __be16 [usertype] <noident>
>> >
>> >drivers/staging/fbtft/fbtft-io.c:74:29: warning: incorrect type in assignment (different base types)
>> >drivers/staging/fbtft/fbtft-io.c:74:29:    expected unsigned long long [unsigned] [long] [long long] [usertype] <noident>
>> >drivers/staging/fbtft/fbtft-io.c:74:29:    got restricted __be64 [usertype] <noident>
>> >
>> >Signed-off-by: simran singhal <singhalsimran0@...il.com>
>> >---
>> >  v2:
>> >    -changed commit message
>> >
>> >  drivers/staging/fbtft/fbtft-bus.c | 2 +-
>> >  drivers/staging/fbtft/fbtft-io.c  | 2 +-
>> >  2 files changed, 2 insertions(+), 2 deletions(-)
>> >
>> >diff --git a/drivers/staging/fbtft/fbtft-bus.c b/drivers/staging/fbtft/fbtft-bus.c
>> >index ec45043..df2223e 100644
>> >--- a/drivers/staging/fbtft/fbtft-bus.c
>> >+++ b/drivers/staging/fbtft/fbtft-bus.c
>> >@@ -163,7 +163,7 @@ int fbtft_write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
>> >                                             to_copy, remain - to_copy);
>> >             for (i = 0; i < to_copy; i++)
>> >-                    txbuf16[i] = cpu_to_be16(vmem16[i]);
>> >+                    txbuf16[i] = vmem16[i];
>>
>> This change breaks functionality on little endian machines like
>> the Raspberry Pi.
>>
>>
>> Noralf.
>>
>
> Hi Simran,
>
> It's probably good to get back to this one while we have Noralf's
> attention.
>
> While the change above - in fbtft-bus.c is a problem, the change
> below in fbtft-io.c looks ok.  So, compare what you did.  You can't
> *not* do the endian conversion.
>
> This is a cleanup change, a cosmetic change.  There is no underlying
> bug, so you just need to get the typing correct w/out affecting
> behavior.
> anyway.
>
> BTW: I think it's OK to pull this one out and send a v3 of this alone.
> That would mean abandoning the patchset and doing them one at a time.
> They are all in different drivers

Hi alison,

Thanks for the explaination.

I will drop the changes I did in fbtft-bus.c and send a v3 of this alone.

Can you please suggest me any source through which I can understand the
concept of endianess. As right know I didn't understand it, I just
tried to fix the
warnings which I got through sparse and as you can see most of the fixes are
wrong.

Thanks!
Simran



> alisons

>
>
>
>> >             vmem16 = vmem16 + to_copy;
>> >             ret = par->fbtftops.write(par, par->txbuf.buf,
>> >diff --git a/drivers/staging/fbtft/fbtft-io.c b/drivers/staging/fbtft/fbtft-io.c
>> >index d868405..ffb9a3b 100644
>> >--- a/drivers/staging/fbtft/fbtft-io.c
>> >+++ b/drivers/staging/fbtft/fbtft-io.c
>> >@@ -71,7 +71,7 @@ int fbtft_write_spi_emulate_9(struct fbtft_par *par, void *buf, size_t len)
>> >                     src++;
>> >             }
>> >             tmp |= ((*src & 0x0100) ? 1 : 0);
>> >-            *(u64 *)dst = cpu_to_be64(tmp);
>> >+            *(__be64 *)dst = cpu_to_be64(tmp);
>> >             dst += 8;
>> >             *dst++ = (u8)(*src++ & 0x00FF);
>> >             added++;
>>
>> --
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