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Message-ID:
<CO6PR18MB40981FD7DB1DA13E851F9EEBB0D02@CO6PR18MB4098.namprd18.prod.outlook.com>
Date: Fri, 28 Jun 2024 13:45:13 +0000
From: Witold Sadowski <wsadowski@...vell.com>
To: Mark Brown <broonie@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"robh@...nel.org"
<robh@...nel.org>,
"krzysztof.kozlowski+dt@...aro.org"
<krzysztof.kozlowski+dt@...aro.org>,
"conor+dt@...nel.org"
<conor+dt@...nel.org>,
"pthombar@...ence.com" <pthombar@...ence.com>
Subject: RE: [EXTERNAL] Re: [PATCH v9 4/9] spi: cadence: Add Marvell SDMA
operations
Hi Mark
>
> > +static void m_ioreadq(void __iomem *addr, void *buf, int len) {
> > + u64 tmp_buf;
> > +
> > + while (len) {
> > + tmp_buf = readq(addr);
> > + memcpy(buf, &tmp_buf, len > 8 ? 8 : len);
> > + len = len > 8 ? len - 8 : 0;
> > + buf += 8;
> > + }
> > +}
>
> Wouldn't it be more efficient and readable to only do the memcpy() for the
> trailing bytes and just do this memcpy() for the final word?
The whole problem is with SDMA end - addr in that case. If code will try to
Read it in non 64b mode, all remaining bits, will be lost.
For example - doing 1B read on that register, will return 1B, but SDMA will
transfer 8B, dropping remaining 7B.
I have tried memcpy approach, and it was not stable.
Regards
Witek
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