linux-kernel - Re: [PATCH] usb: host: xhci: parameterize Renesas delay/retry

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Date:   Mon, 19 Jun 2023 09:59:44 +0000
From:   retpolanne@...teo.net
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Vinod Koul <vkoul@...nel.org>,
        Christian Lamparter <chunkeey@...glemail.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: host: xhci: parameterize Renesas delay/retry

On 19.06.2023 07:46, Greg Kroah-Hartman wrote:
> On Sun, Jun 18, 2023 at 10:46:57PM +0000, Anne Macedo wrote:
>> Cards based on Renesas uPD720202 have their firmware downloaded during
>> boot by xhci-pci. At this step, the status of the firmware is read and
>> it takes a while for this read to happen (up to a few seconds). The
>> macros RENESAS_RETRY and RENESAS_DELAY are used to retry reading this
>> status byte from PCI a few times. If it can't read the status byte in
>> RENESAS_RETRY tries, it times out.
>> 
>> However, since this may vary from card to card, these retry and delay
>> values need to be tweaked. In order to avoid having to patch the code 
>> to
>> change these values, CONFIG_USB_XHCI_PCI_RENESAS_RETRY and
>> CONFIG_USB_XHCI_PCI_RENESAS_DELAY are introduced.
> 
> No, a build-time option that affects all devices controlled by this
> driver is not how you handle this, sorry.

Sorry, I completely forgot that other environments might have multiple 
cards.
Mine only has one and I was focused on making it work.
> 
> Make this a dynamic value, either determined automatically by the 
> device
> itself (as you know what device is being controlled), or worst case, a
> sysfs attribute that you can modify if things are not working properly.
> 

I'll follow Christian's tip and check the uPD720202 user manual and see
if there's something I can look for in order to make this value dynamic.

> But a build-time option will never work, as it will never be changed,
> and it would not allow for multiple devices in the system that are
> different.
> 
> thanks,
> 
> greg k-h