From: Arnd Bergmann <arnd@arndb.de>
To: Alex Elder <elder@linaro.org>
Cc: David Miller <davem@davemloft.net>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Ilias Apalodimas <ilias.apalodimas@linaro.org>,
syadagir@codeaurora.org, mjavid@codeaurora.org,
evgreen@chromium.org, Ben Chan <benchan@google.com>,
Eric Caruso <ejcaruso@google.com>,
abhishek.esse@gmail.com,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 12/18] soc: qcom: ipa: immediate commands
Date: Mon, 20 May 2019 16:50:27 +0200 [thread overview]
Message-ID: <CAK8P3a3161Oc3ALB74LTuDny-aO9E4VGYpmqQSNoDNbj6PhRsQ@mail.gmail.com> (raw)
In-Reply-To: <5d948d74-f739-0cfa-8fae-b15c20fbe7ec@linaro.org>
On Sat, May 18, 2019 at 2:34 AM Alex Elder <elder@linaro.org> wrote:
> On 5/15/19 7:35 AM, Alex Elder wrote:
> > On 5/15/19 3:16 AM, Arnd Bergmann wrote:
> >>
> >> This looks rather strange. I think I looked at it before and you explained
> >> it, but I have since forgotten what you do it for, so I assume everyone else
> >> that tries to understand this will have problems too.
> >
> > This is a bug. I think I misunderstood why you were
> > puzzled before. Now I get it. I need to save that
> > DMA address and not free it at the end of the function
> > (except on error).
>
> OK, now I'm going to correct myself. I hope I don't make
> any mistakes here because things are confused enough...
>
> Part of what I described previously is still true, namely
> there are tables that need to be initialized (i.e., the
> IPA needs to be told where they reside), and there is a
> separate step is available to zero the content of the tables.
>
> But there really is no need for the AP to hang onto this
> DMA memory after this immediate command has been issued.
> I will add comments in the code to make it less surprising.
>
> But here's a summary of why.
>
> I think there are two things at play that make it confusing.
>
> The first thing is that these "header tables" are actually
> located in a region of shared memory ("smem") that is local
> to the IPA (not the AP). The the IPA_CMD_HDR_INIT_LOCAL
> immediate command is meant to:
> 1) define the header table location in IPA local memory
> 2) define the header table size
> 3) provide a buffer used to fill the table with its initial
> contents
>
> The location and size are encoded in the flags field
> of the payload (offset and size).
>
> The initial contents are filled via DMA from a buffer
> in main memory, whose DMA address is supplied in the
> hdr_table_addr parameter in the payload. The initial
> contents we supply are all zero. So this is why we
> need to allocate DMA memory.
>
> The second thing is that this is an instance where the
> AP is responsible for performing some initialization
> of resources it may not "own" thereafter. The IPA
> hardware owns this table, even though the AP needs to
> tell it where it sits in IPA local memory. The AP is
> able to copy (using DMA) content into that table, but
> doing so involves a DMA transfer.
>
> More advanced features of the IPA would make more use
> of this header table, but those features not yet
> supported so this initialization (and a subsequent,
> seemingly redundant zeroing) is all we do.
>
> Does that make sense?
Ok, that sounds reasonable, yes. I'm not sure if
dma_alloc_coherent() guarantees zero-initialization
though, so if that is required, you may have to
add a memset().
Arnd
next prev parent reply other threads:[~2019-05-20 14:50 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-12 1:24 [PATCH 00/18] net: introduce Qualcomm IPA driver Alex Elder
2019-05-12 1:24 ` [PATCH 01/18] bitfield.h: add FIELD_MAX() and field_max() Alex Elder
2019-05-12 6:33 ` Kalle Valo
2019-05-12 12:18 ` Alex Elder
2019-05-12 19:30 ` Johannes Berg
2019-05-12 1:24 ` [PATCH 02/18] soc: qcom: create "include/soc/qcom/rmnet.h" Alex Elder
2019-05-12 2:34 ` Joe Perches
2019-05-12 12:15 ` Alex Elder
2019-05-15 6:59 ` Arnd Bergmann
2019-05-15 12:03 ` Alex Elder
2019-05-16 1:09 ` Subash Abhinov Kasiviswanathan
2019-05-17 17:27 ` Alex Elder
2019-05-17 18:08 ` Subash Abhinov Kasiviswanathan
2019-05-19 17:37 ` Alex Elder
2019-05-12 1:24 ` [PATCH 03/18] dt-bindings: soc: qcom: add IPA bindings Alex Elder
2019-05-15 7:03 ` Arnd Bergmann
2019-05-15 12:04 ` Alex Elder
2019-05-15 16:50 ` Rob Herring
2019-05-15 17:05 ` Alex Elder
2019-05-12 1:24 ` [PATCH 04/18] soc: qcom: ipa: main code Alex Elder
2019-05-12 1:24 ` [PATCH 05/18] soc: qcom: ipa: configuration data Alex Elder
2019-05-12 1:24 ` [PATCH 06/18] soc: qcom: ipa: clocking, interrupts, and memory Alex Elder
2019-05-12 1:24 ` [PATCH 07/18] soc: qcom: ipa: GSI headers Alex Elder
2019-05-12 1:24 ` [PATCH 08/18] soc: qcom: ipa: the generic software interface Alex Elder
2019-05-15 7:21 ` Arnd Bergmann
2019-05-15 12:13 ` Alex Elder
2019-05-15 12:40 ` Arnd Bergmann
2019-05-15 10:47 ` Arnd Bergmann
2019-05-15 13:32 ` Alex Elder
2019-05-15 19:37 ` Arnd Bergmann
2019-05-12 1:24 ` [PATCH 09/18] soc: qcom: ipa: GSI transactions Alex Elder
2019-05-15 7:34 ` Arnd Bergmann
2019-05-15 12:25 ` Alex Elder
2019-05-15 20:50 ` Arnd Bergmann
2019-05-17 18:08 ` Alex Elder
2019-05-17 18:33 ` Arnd Bergmann
2019-05-17 18:44 ` Alex Elder
2019-05-19 17:11 ` Alex Elder
2019-05-20 9:25 ` Arnd Bergmann
2019-05-20 12:50 ` Alex Elder
2019-05-20 14:43 ` Arnd Bergmann
2019-05-20 14:44 ` Alex Elder
2019-05-20 16:34 ` Evan Green
2019-05-20 16:50 ` Alex Elder
2019-05-20 17:36 ` Evan Green
2019-05-12 1:25 ` [PATCH 10/18] soc: qcom: ipa: IPA interface to GSI Alex Elder
2019-05-12 1:25 ` [PATCH 11/18] soc: qcom: ipa: IPA endpoints Alex Elder
2019-05-12 1:25 ` [PATCH 12/18] soc: qcom: ipa: immediate commands Alex Elder
2019-05-15 8:16 ` Arnd Bergmann
2019-05-15 12:35 ` Alex Elder
2019-05-18 0:34 ` Alex Elder
2019-05-20 14:50 ` Arnd Bergmann [this message]
2019-05-20 14:55 ` Alex Elder
2019-05-20 17:35 ` Christoph Hellwig
2019-05-12 1:25 ` [PATCH 13/18] soc: qcom: ipa: IPA network device and microcontroller Alex Elder
2019-05-15 8:21 ` Arnd Bergmann
2019-05-15 12:46 ` Alex Elder
2019-05-12 1:25 ` [PATCH 14/18] soc: qcom: ipa: AP/modem communications Alex Elder
2019-05-12 1:25 ` [PATCH 15/18] soc: qcom: ipa: support build of IPA code Alex Elder
2019-05-12 1:25 ` [PATCH 16/18] MAINTAINERS: add entry for the Qualcomm IPA driver Alex Elder
2019-05-12 1:25 ` [PATCH 17/18] arm64: dts: sdm845: add IPA information Alex Elder
2019-05-12 1:25 ` [PATCH 18/18] arm64: defconfig: enable build of IPA code Alex Elder
2019-05-15 8:23 ` Arnd Bergmann
2019-05-15 12:49 ` Alex Elder
2019-05-15 12:37 ` [PATCH 00/18] net: introduce Qualcomm IPA driver Arnd Bergmann
2019-05-15 12:52 ` Alex Elder
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