Re: [PATCH] dmaengine: qcom: gpi: Set link_rx bit on GO TRE for rx operation

From: Vijaya Krishna Nivarthi
Date: Fri Dec 02 2022 - 12:34:44 EST



On 12/2/2022 4:17 AM, Doug Anderson wrote:
Hi,

On Wed, Nov 30, 2022 at 4:20 AM Vijaya Krishna Nivarthi
<quic_vnivarth@xxxxxxxxxxx> wrote:
As per GSI spec, link_rx bit is to be set on GO TRE on tx
channel whenever there is going to be a DMA TRE on rx
channel. This is currently set for duplex operation only.

Set the bit for rx operation as well.

Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@xxxxxxxxxxx>
---
drivers/dma/qcom/gpi.c | 1 +
1 file changed, 1 insertion(+)
I don't feel qualified to actually give this a review since I don't
know anything about the details of GSI/GPI. It seems simple enough so
I'll just assume that Bjorn will land it. Ideally someone else at
Qualcomm would give you a Reviewed-by tag.

One drive-by comment, though, is that I would say that your patch
description lacks an answer to the question: "So what?"

In other words, what is broken today? Does everything work fine today
but some bit counter looked over your shoulder and told you that you
were a bad person for not setting that bit? Did the lunar lander catch
fire (despite the lack of Oxygen on the moon!) because it started
using the RX transfer mode to talk to its fuel valve system and the RX
transfer mode never worked? ...or maybe everything today works but the
super secret Qualcomm SDM9002 (shhhh!) chip needs this bit set? Help
people looking at your patch be able to decide if it's important for
them to pick to their kernel tree! :-)

:-) Thank you very much for the input. Will keep that in mind for next.


Some info...

rx is actually broken for spi gsi. A plain rx operation would crash right now and patch for same would come next; There are 3 further patches as well for gsi.

I started with simplest patch hoping it would get in quick.

While trying to bring up EC use case with spi gsi, we made some changes to conform to GSI spec, made some progress but still couldn't get it to work.

In the meantime we switched to SE DMA as interim.

-Doug