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Re: [PATCH v2 1/3] hw/block/pflash: Remove dynamic field width from trac

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v2 1/3] hw/block/pflash: Remove dynamic field width from trace events
Date: Mon, 18 Nov 2019 21:39:09 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1

On 11/18/19 8:21 PM, Eric Blake wrote:
On 11/14/19 3:26 PM, Philippe Mathieu-Daudé wrote:

-    trace_pflash_data_read(offset, width << 1, ret);
+    trace_pflash_data_read(offset, width << 3, ret);

Umm, why is width changing?  That's not mentioned in the commit message.

Previously it was used to set the format width: [1, 2, 4] -> [2, 4, 8].

We usually log the width in byte (accessed at memory location) or bits (used by the bus). When using this device I'm custom to think in bus access width.

Regardless whichever format we prefer, a change is needed.

Do you prefer using a "-bit" suffix? As

"offset:0x%04"PRIx64" width:%d-bit value:0x%04x cmd:0x%02x wcycle:%u"

I can also simply remove this information. Ideally I'd revert this patch once the we get this format parsable by the SystemTap backend.

Reporting either 'width:8-bit'/'width:16-bit' (explicit bits) or 'width:1'/'width:2' (implying byte) is fine by me.  Showing a bus width in bytes adequately explains why you are using <<3 (aka converting bits to bytes), and how it compares to the previous <<1 (converting bits to number of hex characters).  But whichever you pick (tracing bit width vs. byte width, and how it differs from previous usage of width as output-character count), documenting it in the commit message will make life easier to understand the change.

Yes you are right, I should have documented to avoid wasting review time clearing the confusion.

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